Methods of fabricating laser-induced graphene and compositions thereof

ABSTRACT

Methods that expand the properties of laser-induced graphene (LIG) and the resulting LIG having the expanded properties. Methods of fabricating laser-induced graphene from materials, which range from natural, renewable precursors (such as cloth or paper) to high performance polymers (like Kevlar). With multiple lasing, however, highly conductive PEI-based LIG could be obtained using both multiple pass and defocus methods. The resulting laser-induced graphene can be used, inter alia, in electronic devices, as antifouling surfaces, in water treatment technology, in membranes, and in electronics on paper and food Such methods include fabrication of LIG in controlled atmospheres, such that, for example, superhydrophobic and superhydrophilic LIG surfaces can be obtained. Such methods further include fabricating laser-induced graphene by multiple lasing of carbon precursors. Such methods further include direct 3D printing of graphene materials from carbon precurors. Application of such LIG include oil/water separation, liquid or gas separations using polymer membranes, anti-icing, microsupercapacitors, supercapacitors, water splitting catalysts, sensors, and flexible electronics.

RELATED PATENT APPLICATIONS

The application claims priority to the following provisional patentapplications: (a) U.S. Patent Application No. 62/418,202, entitled“Polymer-Derived Laser-Induced Graphene Materials And Uses Thereof,”filed on Nov. 6, 2016,); (b) U.S. Patent Application No. 62/487,821,entitled “Methods of Fabricating Laser-Induced Graphene In ControlledAtmospheres And Compositions Thereof,” filed Apr. 20, 2017; and (c) U.S.Patent Application No. 62/537,512 entitled “Polymer-DerivedLaser-Induced Graphene Materials And Uses Thereof,” filed Jul. 27, 2017.All of these above-identified applications are commonly assigned to theApplicants of the present invention and are hereby incorporated hereinby reference in their entirety for all purposes.

GOVERNMENT INTEREST

This invention was made with government support under Grant No.FA9550-14-1-0111 and FA9550-12-1-0035, awarded by the U.S. Department ofDefense, Air Force Office of Scientific Research. The United Statesgovernment has certain rights in the invention.

FIELD OF INVENTION

The present invention relates to methods of fabricating laser-inducedgraphene from materials, which range from natural, renewable precursors(such as cloth or paper) to high performance polymers (like Kevlar). Theresulting laser-induced graphene can be used, inter alia, in electronicdevices, as antifouling surfaces, in water treatment technology, and inelectronics on paper and food.

BACKGROUND OF INVENTION

Graphene, an important member of the family of carbon nanomaterials, hasshown promising applications in electronic devices, energy storage, andelectrochemical catalysis due to its unique physical properties such ashigh surface area, high conductivity, good mechanical strength andstability. [Geim 2007; Geim 2009; Allen 2009; James 2012; Novoselov2012; Lee 2008; Bolotin 2008; Balandin 2008; Lin 2010; Dai 2012; Fan2015]. The modification of graphene structures introduces functionalgroups and/or active substances onto the graphene surface or edges, thusproviding varied materials properties. Common structural changes ongraphene generally occur post-graphene formation, and they involvewet-chemical or chemical vapor deposition (CVD) processes. [Liu 2012;Georgakilas 2012; Hirsch 2012; Wang 2014].

An often-desired modification of graphene seeks to tune thehydrophilicity or hydrophobicity of the surface of graphene-basedmaterials, especially to achieve superhydrophobic surfaces that can beused for applications such as water and oil separation [Nguyen 2012;Dong 2012; Hu 2014; Feng 2016; Ma 2016] or anti-icing [Wang 2016]. Thespecific approaches include sonicating graphene oxide (GO) in differentsolvents followed by drop-coating [Rafiee 2010], dip-coating of spongeswith thermally shocked GO [Nguyen 2012], CVD synthesis of 3Dgraphene/CNT hybrids [Dong 2012], microwave-assisted synthesis ofgraphene/CNT aerogels [Hu 2014], and by introducing fluorine-groups intothe graphene-based structures or surfaces. [Wang 2016; Lin 2011; Zha2011; Singh 2013; Li 2014]. These involve coating graphene foam or gelwith polyvinylidene difluoride (PVDF) or polytetrafluoroethylene(Teflon™) [Zha 2011; Singh 2013; Li 2014], modifying GO aerogels withperfluorodecyltrichlorosilane [Lin 2011], and functionalizing graphenenanoribbons (GNRs) with perfluorododecyl groups [Wang 2016], all ofwhich exploit the lower surface energy of C—F bonds to achieve evenhigher contact angles. Yet, within all the methods reported, usuallymultiple steps are required to yield the desired materials, and they alloccur post-graphene formation.

Recently, the inventors of the present invention reported alaser-induced graphene (LIG) method as a facile and scalable approach toproduce 3D porous graphene structures through a one-step laser scribingprocess from commercial polyimide (PI, Kapton®) films, which can bedirectly used as electrode materials for interdigitatedmicrosupercapacitors, among other potential applications. [Lin 2014;Peng I 2015]. Various methods have then been developed to tune orimprove the physical and chemical properties of the LIG by varying thelaser conditions to change the thickness and morphology of LIG, or byintroduction of boron or metal doping in the LIG by mixing the PIprecursor with other substances. [Peng II 2015; Ye 2015]. Furthermore,modification can be done through the electrochemical deposition ofactive materials on top of the original LIG layer for high-performancepseudo-supercapacitors. [Li 2014]. Yet, all these LIG materials werefabricated in ambient atmosphere, and the surfaces that were producedwere always hydrophilic, which allowed better contact between thegraphene structures and the water-based electrolytes.

Porous 3D graphene-based nanomaterials demonstrate promise for a widevariety of applications due to their unique physical and chemicalproperties. A straightforward method of synthesizing laser-inducedgraphene (LIG) from polyimide (PI, Kapton®) has been previously reportedand applied towards energy storage devices such as supercapacitors [Ye2014], electrocatalysts for water splitting [Zhang 2017], piezoelectricstrain gauges [Rahimi 2015], and for electrochemical biosensors [Rahimi2015]. A limitation of this approach has been the reliance on polyimideas the polymer precursor for the formation of LIG.

The modification of graphene-based materials is an important topic inthe field of materials research. The need remains to expand the range ofproperties for LIG.

SUMMARY OF INVENTION

The present invention provides a method to form LIG from a wide varietyof carbon precursors including polymers, natural materials, and evennon-polymeric materials such as activated carbon or anthracite coal bymeans of multiple lasing. Multiple lasing allows enhancement of theelectrical properties by improving the quality of the LIG obtained. Forexample, polyetherimide (PEI) was previously found to produce LIG thatwas substantially less conductive than that formed from PI. [Lin 2014].With multiple lasing, however, highly conductive PEI-based LIG could beobtained using both multiple pass and defocus methods. Moreover,multiple lasing allows for the formation of LIG on naturally occurringsubstrates such as cloth, paper, potato skins, coconut shells, cork, andactivated carbon. These materials are inexpensive, abundant, andbiodegradable unlike many of the polymer precursors found to yield LIG.The ability to form LIG on these substrates would potentially allow newapplications such as flexible micro-supercapacitors on cloth or evenedible electronics (after a thorough toxicity study).

The present invention expands the range of properties for laser-inducedgraphene (LIG), specifically to tune the hydrophobicity andhydrophilicity of the LIG surfaces. While LIG is normally prepared inthe air, here, using selected gas atmospheres, a large change in thewater contact angle on the as-prepared LIG surfaces has been observed,from 00 (superhydrophilic) when using O₂ or air, to >1500(superhydrophobic) when using Ar or H₂. Characterization of the newlyderived surfaces shows that the different wetting properties are due tothe surface morphology and chemical composition of the LIG. Applicationsof the superhydrophobic LIG are shown in oil/water separation as well asanti-icing surfaces, while the versatility of the controlled atmospherechamber fabrication method is demonstrated through the improvedmicrosupercapacitor performance generated from LIG films prepared in anO₂ atmosphere.

In other embodiments, the present invention relates to a laser-inducedgraphene made by multiple lasing of carbon precursors, which is animprovement to U.S. Patent Appl. Publ. No. 2017/0061821, entitled “LaserInduced Graphene Materials And Their Use In Electronic Devices,” filedFeb. 17, 2015, to J. M. Tour et al. (the “Tour '821 application”)(co-owned by one of the Applicants), by further expanding theapplicability of the lasing technique to generate laser-inducedgraphene. (The Tour “821 application is the § 371 filing of PCTInternational Application Publ. No. WO/2015/175060, and is incorporatedherein in its entirety). ‘The present invention allows for theconversion of other carbon precursors beyond the previously reportedformation of graphene from a polymer. With the methods of the presentinvention, carbon precursors other than the previously reportedpolyimide (PI) and polyetherimide (PEI) can be converted intolaser-induced graphene materials, such as various aromatic polymers,lignin-containing materials, cellulose-based materials, andnon-polymeric sources of carbon.

Some of the aromatic polymers that have been converted to laser-inducedgraphene by this method include polymers such as polyphenylene sulfide,polyamide-imide, polybenzimidazole, phenol-formaldehyde resin,poly(ether ether ketone) (PEEK), polysulfone, polyether sulfone,polyphenylsulfone, poly(m-pheylenediamine) isopthalamide, crosslinkedpolystyrene, epoxy, and poly(ether-imide). Lignin-containing materialsinclude wood, coconut shells, potato skins, and burlap (jute fibers).Cellulose-based materials to promote LIG formation include cotton cloth,paper, cardboard (including those that are catalyst treated).Non-polymeric sources of carbon include amorphous carbon, charcoal,biochar, activated carbon, cole, asphalt, coke, and Gilsonite. Each ofthese can be employed to obtain LIG using the method of the presentinvention.

Previously, studies showed that only polymers containing aromatic andimide structures were reliably converted to porous graphene by laserscribing. The present invention is a laser scribing method for theproduction of graphene that can be generally applied to most carbonprecursors. The method of the present invention also applies tonon-polymeric materials, such as amorphous carbons, biochar, activatedcarbon, activated charcoal, coal and most other carbon sources.

In further embodiments, the present invention relates to direct 3Dprinting (more recently called additive manufacturing) of graphenematerials from carbon precursors. The present invention includes ametal-free method by which a 3D graphene object can be printed via theexposure of one or more carbon precursors to laser irradiation. Singleexposures of a laser can be employed, but, preferably, multipleexposures would be used.

Previous methods for obtaining 3D graphene typically involved 3Dprinting from GO inks or the thermal conversion of a carbon source suchas sucrose by a metal catalyst such as nickel; the latter constitutes apowder metallurgy technique and not a 3D printing technique. And in thatcase a freestanding graphene object could only be obtained by a solutionetch of the metal catalyst.

This present invention allows for the direct 3D printing of graphenefrom one or more carbon precursors including at least one polymer byusing the multiple lase technique previously described. One potentialembodiment of this process is the multiple lasing of a mixture ofpoly(phenylene sulfide) (PPS) and activated carbon (AC) powder by eitherthe multiple scan or defocused raster methods. The combination of thesematerials and use of the multiple laser procedure in the 3D print allowsan extremely conductive material with a sheet resistance of <5Ohm/square to be obtained under certain parameters. Because the processis metal-free, both metal catalysts and non-metal additives can be addedin controlled amounts to tune the properties of the 3D graphene forvarious applications.

In general, in one embodiment, the invention features a method ofproducing a graphene material. The method includes selecting a materialincluding a carbon precursor. The method further includes converting thecarbon precursor into laser-induced graphene by utilizing a laser havinga focal plane to subject the carbon precursor to more than one exposureof laser irradiation. The step of utilizing the laser is selected fromthe group consisting of (i) utilizing the laser to perform multiple lasepasses over a same area of the material, (ii) utilizing the laser uponoverlapping regions of lased areas of the material, and (iii)combinations thereof.

Implementations of the invention can include one or more of thefollowing features:

The step of converting the carbon precursor into laser-induced graphenecan be performed at ambient conditions.

The method can further include applying a heat source to the material tochar the carbon precursor before the step of converting carbon precursorinto laser-induced graphene.

The heat source can be a flame.

The material including the carbon precursor can be selected from a groupconsisting of polymers, lignin-containing materials, cellulose-basedmaterials, and non-polymeric sources of carbon.

The material including the carbon precursor can be an polymer selectedfrom a group consisting of polyphenylene sulfide, polyamide-imide,polybenzimidazole, phenol-formaldehyde resin, poly(ether ether ketone)(PEEK), poly(m-pheylenediamine) isopthalamide, crosslinked polystyrene,epoxy, and poly(ether-imide).

The material including the carbon precursor can be a lignin-containingmaterial selected from a group consisting of wood, coconut shells,potato skins, and burlap.

The material including the carbon precursor can be a cellulose-basedmaterial selected from a group consisting of cotton cloth, paper, cottonpaper, and cardboard.

The material including the carbon precursor can be a non-polymericsource of carbon selected from a group consisting of amorphous carbon,charcoal, biochar, activated carbon coal, asphalt, coke, and Gilsonite.

The step of converting the carbon precursor into laser-induced graphenecan include utilizing the laser to perform multiple lase passes over thesame area of the material with the material positioned in the focalplane of the laser.

The step of converting the carbon precursor into laser induced-graphenecan include utilizing the laser upon the overlapping regions of lasedareas of the material with the material positioned offset the focalplane of the laser.

The laser can be utilized at ambient conditions.

The utilization of the laser can include exposing the material tomultiple lases in a single pass of the laser while the material ispositioned offset the focal plane of the laser.

The material can be positioned offset of the focal plane of the laser inan amount that is at least 1% of the laser focal length.

The material can be positioned offset of the focal plane of the laser inan amount that is at least 2% of the laser focal length.

In general, in another embodiment, the invention features a method ofproducing a graphene material. The method includes controlling a gasatmosphere. The method further includes fabricating laser-inducedgraphene by exposing one or more carbon precursors to a laser source inthe controlled atmosphere. The exposing results in formation oflaser-induced graphene derived from the one or more carbon precursors.

Implementations of the invention can include one or more of thefollowing features:

The step of controlling the gas atmosphere can obtain a superhydrophiliclaser-induced graphene or a highly hydrophilic laser-induced graphene.

The step of controlling the gas atmosphere can obtain a superhydrophobiclaser-induced graphene or a highly hydrophobic laser-induced graphene.

The step of controlling the gas atmosphere can include a gas assistmethod in which a first gas is blown directly at the laser spot of thelaser source while the one or more carbon precursors are surrounded byair.

The step of controlling the gas atmosphere can include utilizing acontrolled atmosphere chamber.

The controlled gas atmosphere can use O₂ or air. The laser-inducedgraphene can be a superhydrophilic laser-induced graphene.

The controlled gas atmosphere can use at least one of nitrogen, argon,SF₆, and H₂. The laser-induced graphene can be a superhydrophobiclaser-induced graphene.

The controlled gas atmosphere can include an inert gas.

The inert gas can be selected from a group consisting of nitrogen andargon.

The controlled gas atmosphere can include a reactive gas.

The reactive gas can be a halogenated gas.

The halogenated gas can be selected from a group consisting of Cl₂, Br₂,SF₆, and XeF₂.

The reactive gas can be a reducing gas.

The reducing gas can be selected from a group consisting of H₂ and NH₃.

The reactive gas can be an oxidizing gas.

The oxidizing gas can be selected from a group consisting of O₂ and air.

The reactive gas can be selected from the group consisting of CO, SO₂,and NO₂.

In general, in another embodiment, the invention features a materialincluding laser-induced graphene made by at least one of theabove-described methods.

In general, in another embodiment, the invention features a method thatincludes selecting an above-described material including laser-inducedgraphene. The method further includes utilizing the laser-inducedgraphene in an application selected from a group consisting of water/oilseparation processes and anti-icing processes.

In general, in another embodiment, the invention features a method ofproducing a graphene material. The method includes selecting one or morecarbon precursors. The method further includes fabricating laser-inducedgraphene by exposing the one or more carbon precursors to more than onelase.

Implementations of the invention can include one or more of thefollowing features:

The one or more carbon precursors can not include polyimide (PI) andpolyetherimide (PEI).

At least one of the one or more carbon precursors can be selected from agroup consisting of aromatic polymers, lignin-containing materials,cellulose-based materials, and non-polymeric sources of carbon.

At least one of the one or more carbon precursors can be an aromaticpolymer selected from a group consisting of polyphenylene sulfide,polyamide-imide, polybenzimidazole, phenol-formaldehyde resin,poly(ether ether ketone) (PEEK), poly(m-pheylenediamine) isopthalamide,crosslinked polystyrene, epoxy, and poly(ether-imide).

At least one of the one or more carbon precursors can be alignin-containing material selected from a group consisting of wood,coconut shells, potato skins, and burlap.

At least one of the one or more carbon precursors can be acellulose-based material selected from a group consisting of cottoncloth, paper, and cardboard.

The cellulous-based material can be a catalyst treated cellulousmaterial.

The cellulous material can be pre-treated with a flame retardant beforethe step of fabricating the laser-induced graphene.

The flame retardant can be a phosphate-based retardant or a borate-basedflame retardant.

The cellulous-based material can be been pretreated by charring thecellulous-based material before the step of fabricating thelaser-induced graphene.

At least one of the one or more carbon precursors can be a non-polymericsource of carbon selected from a group consisting of amorphous carbon,charcoal, biochar, activated carbon coal, asphalt, coke, and Gilsonite.

The step of fabricating the laser-induced graphene can include exposingthe one or more carbon precursors to more than one lase at multiple lasespots that do not overlap.

The step of fabricating the laser-induced graphene can include exposingthe one or more carbon precursors to more than one lase at multiple lasespots that do overlap.

The method can further include a step selected from a group consistingof: (a) performing the step of fabricating the laser-induced graphenewhile controlling the reaction atmosphere; (b) converting surface of theone or more carbon precursors into amorphous or graphitic carbons bythermal or chemical means; (c) applying a char promoting catalyst topromote the formation of amorphous or graphitic carbons; and (d)combinations thereof.

The method can further include controlling the reaction atmosphere whileperforming the step of fabricating the laser-induced graphene.

The controlled gas atmosphere can include an inert gas.

The inert gas can be selected from a group consisting of nitrogen andargon.

The controlled gas atmosphere can include a reactive gas.

The reactive gas can be selected from a group consisting halogenatedgases, reducing gases, and oxidizing gases.

The reactive gas can be selected from the group consisting of Cl₂, Br₂,SF₆, XeF₂, H₂, NH₃, O₂, air, CO, SO₂, and NO₂.

The method can further include adding a metal solution to thelaser-induced graphene. The metal solution can be selected from a groupconsisting of metal salt solutions, metal oxide solutions, and metalnanoparticle solutions, and combinations thereof. The method can furtherinclude exposing the laser-induced graphene with the added metalsolution to one or more lases.

The step of exposing the laser-induced graphene with the added metalsolution to one or more lases can form nanoparticles dispersed in thelaser-induced graphene. The nanoparticles can be selected from a groupconsisting of metal nanoparticles, metal carbide nanoparticles, metaloxide nanoparticles, and combinations thereof.

The metal solution can include a metal selected from a group consistingof Co, Ni, Pt, Pd, Fe, Ru, transition metals, mixtures of transitionmetals and main group elements, and combinations thereof.

The main group elements can be chalcogenides or phosphides.

The metal solution can include a cobalt phosphide or a nickel phosphide.

In general, in another embodiment, the invention features a method ofproducing a graphene material. The method includes selecting one or morecarbon precursors. The method further includes fabricating laser-inducedgraphene by exposing the one or more carbon precursors to thermal orchemical charring followed by a one lase cycle or greater than one lase.

Implementations of the invention can include one or more of thefollowing features:

At least one of the one or more carbon precursors can be selected from agroup consisting of polymers lignin-containing materials,cellulose-based materials, and non-polymeric sources of carbon.

At least one of the one or more carbon precursors can be an aromaticpolymer selected from a group consisting of polyphenylene sulfide,polyamide-imide, polybenzimidazole, phenol-formaldehyde resin,poly(ether ether ketone) (PEEK), poly(m-pheylenediamine) isopthalamide,crosslinked polystyrene, epoxy, and poly(ether-imide).

At least one of the one or more carbon precursors can be alignin-containing material selected from a group consisting of wood,coconut shells, potato skins, and burlap.

At least one of the one or more carbon precursors can be acellulose-based material selected from a group consisting of cottoncloth, paper, and cardboard.

At least one of the one or more carbon precursors can be a non-polymericsource of carbon selected from a group consisting of amorphous carbon,charcoal, biochar, activated carbon, coal, asphalt, coke, and Gilsonite.

The one or more carbon precursors can be in the form of a roll such thatthe step of fabricating the laser-induced graphene can be performed in aroll-to-roll process.

The one or more carbon precursors can be selected from a groupconsisting of paper, cotton paper, cardboard, and polymer films.

The step of fabricating the laser-induced graphene can be performedutilizing a roll-to-roll process.

In general, in another embodiment, the invention features alaser-induced graphene made by at least one of the above-describedmethods.

In general, in another embodiment, the invention features a method thatincludes selecting an above-described laser-induced graphene. The methodfurther includes utilizing the laser-induced graphene in an applicationselected from a group consisting of water/oil separation processes,anti-icing processes, microsupercapacitors, supercapacitors,electrocatalysis, water splitting catalysts, sensors, and flexibleelectronics.

In general, in another embodiment, the invention features a method thatincludes irradiating a material including an aromatic polysulfone with alaser to form laser-induced graphene on the surface of the materialincluding the aromatic polysulfone.

Implementations of the invention can include one or more of thefollowing features:

The aromatic polysulfone can be selected from a group consisting ofpolysulfone, polyethersulfone, and polyphenylsulfone.

The method can further include a step of separating the laser-inducedgraphene from the material.

In general, in another embodiment, the invention features a materialthat includes an aromatic polysulfone having graphene on a surface ofthe material.

Implementations of the invention can include one or more of thefollowing features:

The material can include the aromatic polysulfone having sulfur-dopedgraphene on the surface of the material.

In general, in another embodiment, the invention features a method ofreducing microbial load in a bulk solution. The method includes placingelectrodes in the bulk solution. The electrodes include graphenerecovered from laser-irradiated aromatic polysulfone. The method furtherincludes applying a voltage across the electrodes.

In general, in another embodiment, the invention features a method oftreating a surface prone to the formation of biofilm. The methodincludes applying a carbon precursor onto the surface to form a carbonprecursor-coated surface. The method further includes laser-irradiatingthe carbon precursors-coated surface to form graphene thereon thesurface.

In general, in another embodiment, the invention features a method oftreating a surface prone to the formation of biofilm. The methodincludes laser-irradiating a material including a carbon precursor toform laser-induced graphene thereon. The method further includes coatingthe surface with the laser-irradiated material including thelaser-induced graphene.

In general, in another embodiment, the invention features a method oftreating a surface prone to the formation of biofilm. The methodincludes identifying a portion of the surface that includes a carbonprecursor. The method further includes laser-irradiating the portion ofthe surface to form graphene from the carbon precursor thereon thesurface.

In general, in another embodiment, the invention features a method thatincludes utilizing laser-induced graphene in a process selected from agroup consisting of (a) for coating the inside of a pipe, (b) fordegradation of organic or inorganic pollutants, (c) for a component ofmembrane water treatment equipment, (d) a component in a medicalapplication and (d) combinations thereof.

Implementations of the invention can include one or more of thefollowing features:

The process for degradation of organic or inorganic polutants caninclude oxidizing organic contaminents by applying electrical voltage tothe laser-induced graphene.

The component of the membrane water treatment equipment can be selectedfrom a group consisting of a membrane spacer operable for adsorption ofpollutants, laser-induced graphene attached to a substrate,laser-induced graphene separated from a substrate, and laser-inducedgraphene attached to a membrane of the membrane water treatmentequipment.

The medical application can be a blood dialysis application.

The blood dialysis application can utilize a dialysis membrane thatincludes the laser-induced graphene.

In general, in another embodiment, the invention features a method offabricating a membrane for a separation application. The method includesselecting a membrane having a carbon precursor layer. The method furtherincludes generating laser-induced graphene on the carbon precursor layerof the membrane to form a laser-induced graphene-coated separationmembrane.

Implementations of the invention can include one or more of thefollowing features:

The separation application can be selected from a group consisting ofoil/water separation, liquid separations, gas separations, andliquid/gas separations.

The membrane can be a polymer membrane.

The carbon precursor can be an aromatic polysulfone.

The aromatic polysulfone can be selected from a group consisting of ofpolysulfone, polyethersulfone, and polyphenylsulfone.

In general, in another embodiment, the invention features a method thatincludes using a stack of at least two laser-induced graphene-coatedmembranes for filtration. Each of the at least two laser-inducedgraphene-coated membranes includes a surface having laser-inducedgraphene. The method further includes utilizing the laser-inducedgraphene surfaces as electrodes during a filtration process.

In general, in another embodiment, the invention features a method thatincludes selecting a material including laser-induced graphene. Themethod further includes utilizing the material including laser-inducedgraphene in a water treatment process.

Implementations of the invention can include one or more of thefollowing features:

The laser-induced graphene can include laser-irradiated aromaticpolysulfone.

The method can further include laser-irradiating a material including anaromatic polysulfone to form the material including laser-inducedgraphene.

In general, in another embodiment, the invention features a method thatincludes selecting a material including laser-induced graphene. Themethod further includes utilizing the material including laser-inducedgraphene in a membrane separation process.

Implementations of the invention can include one or more of thefollowing features:

The method can further include utilizing the material includinglaser-induced graphene in which an electrical voltage is applied.

The electrical voltage can be direct current (DC) or alternating current(AC).

In general, in another embodiment, the invention features a method thatincludes selecting a laser-induced graphene having dispersednanoparticles selected from a group consisting of metal nanoparticles,metal carbide nanoparticles, metal oxide nanoparticles, and combinationsthereof. The method further includes utilizing the laser inducedgraphene having dispersed nanoparticles as a catalyst in a reaction.

Implementations of the invention can include one or more of thefollowing features:

The reaction can be selected from a group consisting of organicoxidation or reduction transformations and electrocatalytictransformations.

The electrocatalytic transformations can be selected from a groupconsisting of hydrogen evolution reactions (HER), oxygen evolutionreactions (OER), hydrogen oxidation reactions (HOR), oxygen reductionreactions (ORR), and combinations thereof.

In general, in another embodiment, the invention features a method thatincludes selecting one or more carbon precursors. The method furtherincludes direct 3D printing of graphene materials from the one or morecarbon precursors via the exposure of the one or more carbon precursorsto laser irradiation. The laser irradiation is performed utilizing alaser having a focal plane. The step of utilizing the laser is selectedfrom the group consisting of (i) utilizing the laser to perform multiplelase passes over a same area of the material, (ii) utilizing the laserupon overlapping regions of lased areas of the material, and (iii)combinations thereof.

Implementations of the invention can include one or more of thefollowing features:

A metal catalyst can not be required to produce the graphene materialsfrom the one or more carbon precursors.

The step of 3D printing can not utilize a metal catalyst.

The method can be a metal-free 3D printing process.

The exposure of the one or more carbon precursors to the laserirradiation can include multiple exposures.

The one or more carbon precursors can include a mixture of at least twodifferent carbon precursors.

The two different carbon precursors can include a polymer and activatedcarbon.

The two different carbon precursors can include a thermoplastic carbonprecursor and a non-thermoplastic carbon precursor.

At least one of the one or more carbon precursors can be selected from agroup consisting of aromatic polymers, lignin-containing materials,cellulose-based materials, and non-polymeric sources of carbon.

The method can further include a step selected from a group consistingof: (a) exposure of the one or more carbon precursors to the laserirradiation is performed while controlling the reaction atmosphere; (b)mixing an additive into the one or more carbon precursors; (c) at leastone of the one or more carbon precursors is a liquid carbon precursor;and (d) combinations thereof.

The additive can be selected from a group consisting of melamine,ammonia, boranes, phosphenes, phosphides, and combinations thereof.

The exposure of the one or more carbon precursors to the laserirradiation can be performed while controlling the reaction atmosphere.

The exposure of the one or more carbon precursors to the laserirradiation can be performed utilizing the laser to perform multiplelase passes over the same area of the material. The material can bepositioned in the focal plane of the laser.

The exposure of the one or more carbon precursors to the laserirradiation can be performed utilizing the laser in which the one ormore carbon precursors are irradiated offset of the focal plane of thelaser.

The laser can have a laser focal length. The offset of the focal planeof the laser can be in an amount that is at least 1% of the laser focallength.

The offset of the focal plane of the laser can be in an amount that isat least 1.5% of the laser focal length.

The offset of the focal plane of the laser can be in an amount that isat least 2% of the laser focal length.

In general, in another embodiment, the invention features a 3D graphenestructure made by at least one of the above-described methods.

In general, in another embodiment, the invention features a 3D printingapparatus that include a build area. The 3D printing apparatus furtherincludes a laser positioned adjacent to the build area operable to movein a first direction and a second direction. The first direction and thesecond direction are orthogonal. The 3D printing apparatus furtherincludes a reservoir including a material that can be amorphous carbonor can be converted to amorphous carbon. The 3D printing apparatusfurther includes a distributor operable to distribute the material intothe build area. The laser is operable to irradiate the material to formlaser-induced graphene. The build area is operable to be moved in athird direction that is orthogonal to the first direction and the seconddirection. The 3D printing apparatus is operable to print a 3D object bythe irradiation of the material performed in conjunction with themovements of the build area in the third direction and the movement ofthe laser in the first direction and the second direction.

Implementations of the invention can include one or more of thefollowing features:

The reservoir can include a material that can be converted to amorphouscarbon.

The foregoing has outlined rather broadly the features and technicaladvantages of the invention in order that the detailed description ofthe invention that follows may be better understood. Additional featuresand advantages of the invention will be described hereinafter that formthe subject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and the specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of theinvention. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention as set forth in the appended claims.

It is also to be understood that the invention is not limited in itsapplication to the details of construction and to the arrangements ofthe components set forth in the following description or illustrated inthe drawings. The invention is capable of other embodiments and of beingpracticed and carried out in various ways. Also, it is to be understoodthat the phraseology and terminology employed herein are for the purposeof the description and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F relate to lignin LIG on coconut shell. FIG. 1A is picture ofLIG patterned into a Rice logo on a coconut. FIG. 1B is a Raman spectraof coconut-derived LIG lased at two times at 10% speed 5% power. FIG. 1Cis a low resolution TEM of coconut-derived LIG after 5 lases. The scalebar is 50 nm. FIG. 1D is a high resolution TEM coconut-derived LIG (10%speed, 5% power, 5×) showing the characteristic 0.34 nm d-spacing ofgraphene. The scale bar is 5 nm. FIG. 1E is a LIG on cork in the shapeof an owl. FIG. 1A is a potato scribed with laser to form LIG in “R”pattern.

FIGS. 2A-2B are TEM images of a laser-scribed coconut shell (singlelase).

FIG. 3 is an IR spectrum of amorphous carbon and laser-induced graphenederived from cork.

FIGS. 4A-4C relate to activated carbon and activated carbon LIG. FIG. 4Ais a TEM of activated carbon lased one time at 5% speed 5% power. FIG.4A is an activated carbon lased 5× at 5% speed 5% power showing presenceof few layer graphene. FIG. 4C is a Raman spectra of activated carbonLIG lased 2×at 5% speed 5% power with ˜0.25 mm defocus.

FIGS. 5A-5B relate to spot size vs defocus. FIG. 5A is a diagram ofdefocusing on the substrate to increase the laser spot size such thatlaser shots overlap, resulting in multiple exposures. FIG. 5B is a graphshowing the equivalent number of lases at various defocus.

FIGS. 6A-6D related to PEI sheet resistance and Raman spectra as afunction of defocus. FIG. 6A is a Raman spectra of PEI-LIG at variousdefocus values ranging from 0.0 mm to ˜2.0 mm (10% speed 5% power), withcurves 601-605 corresponding to 0.00 mm, 0.25 mm, 0.76 mm, 1.27 mm, and1.78 mm, respectively. FIG. 6B is sheet resistance, measured using4-point probe, of PEI-LIG at various levels of defocus. FIG. 6C is asummary of I_(D)/I_(G) and I2_(D)/I_(G) of PEI-LIG for various amountsof defocus. FIG. 6D is a summary of the FWHM of the G peak for variousamounts of defocus.

FIG. 7A is an optical image of Whatman filter paper at 20×magnification. Scale bar is 50 μm.

FIG. 7B is an optical image of charred Whatman filter paper at 50×magnification. Scale bar is 50 μm.

FIG. 7C is an optical image of LIG from lased Whatman filter paper at50× magnification. Scale bar is 50 μm.

FIGS. 8A-8D are optical images of other cellulose containing materials(canvas, denim, jute (burlap), and muslin cloth respectively) that weretreated with phosphate catalysts and then lased to form LIG. Scale baris 200 μm.

FIGS. 9A-9D relate to LIG on various materials. FIG. 9A is a photographsof the letter “R” in LIG induced from phosphate fire retardant treatedbread. FIG. 9B LIG is a photograph of a fire-retardant treated 2×4 andon a cardboard box. FIG. 9C is a photograph of LIG in the shape of anowl on cotton paper. FIG. 9D is a photograph of LIG in the shape of anowl on a pizza box.

FIG. 10A is a scheme for the fabrication of LIG with gas assist where astream of air or H₂/Ar is blown across the surface of the PI without acontrolled atmosphere chamber.

FIGS. 10B-10C are schemes for the fabrication of LIG inside a controlledatmosphere chamber.

FIG. 10D is an actual photo of a home-built controlled atmospherechamber used in embodiments of the present invention. The schematicdesign is shown in FIGS. 15A-15B.

FIGS. 10E-10J are top view SEM images of LIG samples prepared underdifferent gas atmospheres. Gas assist: (FIG. 10E) air, (FIG. 10F) 3%H₂/Ar. Controlled atmosphere chamber: (FIG. 10G) O₂, (FIG. 10H) air,(FIG. 10I) Ar, (FIG. 10J) H₂. Scale bars: 2 μm. Inset pictures in FIGS.10E-10J are the water droplet appearance on the LIG surfaces. (FIG.10F-10H) The water droplet appears to have a contact angle of 0°, (i)152°, (j) 157°. SEM images with lower magnification are shown in FIGS.16A-16L (top views and side views). 2% laser duty cycle is used forthese samples.

FIG. 11 is a graph showing contact angles of LIG samples prepared underdifferent gas atmospheres with different laser duty cycles. The dashedline at 1500 is the minimum contact angle required forsuperhydrophobicity. The first column is done with air assist or with O₂in the chamber, and the second column is done with 3% H₂/Ar assist. Therest of the columns are done with Ar or H₂ in the chamber. The errorbars reflect the difference between various spots of the same sample.

FIGS. 12A-12B are XPS spectra for LIG samples made under different gasatmospheres with (FIG. 12A) Normalized C 1s spectra, (FIG. 12B) O 1sspectra.

FIG. 12C is a graph showing the relationship between water contact angle(bars), O content (red dots), and C—O bond content (of total O content,blue circles) for LIG samples made under different gas atmospheres. 2%laser duty cycle is used for these samples. For the calculation of C—Ocontent (relative to total O content, i.e. total of C—O and C═Ocontent), the C—O peak was assigned at 533.4 eV and the C═O peak wasassigned at 532.3 eV for the deconvolution. [Hontoria-Lucas 1995; Bagri2010]

FIG. 12D is the Raman spectra for LIG samples made under different gasatmospheres.

FIG. 12E is a graph showing the relationship between contact angle(bars), D/G ratio (red dots), and 2D/G ratio (blue circles) for LIGsamples made under different gas atmospheres. 2% laser duty cycle isused for these samples. The error bars reflect the difference betweenvarious spots of the same sample.

FIGS. 13A-13F show the characterization of LIG made with an atmosphereof SF₆ in the chamber. FIG. 13A is a top-view SEM image; the inset isthe water droplet on the LIG surface with a contact angle of 162°. FIG.13B is the Raman spectrum. FIG. 13C is the XPS survey spectrum. FIG. 13Dis the C 1s spectrum. FIG. 13E is the F 1s spectrum. FIG. 13F 1s the S2p spectrum. Additional SEM and TEM images are shown in FIGS. 26A-26C. A9.3 μm CO₂ laser was used when SF₆ was present. A 4% laser duty cycle isused for this sample.

FIGS. 14A-14D show performance of microsupercapacitors prepared from LIGwith O₂ in the chamber vs air in the chamber. FIG. 14A shows the CVcurves with a scan rate of 10 mV/s. FIG. 14B shows the charge/dischargecurves with a current density of 0.5 mA/cm². FIG. 14C shows the specificcapacitance plotted against current density. FIG. 14D shows the Ragoneplot showing the energy and power densities of the devices.

FIGS. 15A-15B are drawings of the top view and side view drawings of thehome-built controlled atmosphere chamber shown in FIG. 10D.

FIGS. 16A-16L are (FIGS. 16A-16F) top view and (FIGS. 16G-16L) side viewSEM images of LIG made under different gas atmosphere. 2% laser dutycycle is used for these samples. The scale bar is 50 μm for all images.

FIGS. 17A-17B are high resolution SEM images of (FIG. 17A) LIG with H₂(chamber) and (FIG. 17B) LIG with O₂ (chamber). Scale bars: 500 nm.

FIGS. 18A-18B are TEM images of (FIG. 18A) aggregated carbonnanoparticles and (FIG. 18B) aggregated carbon nanoparticles on thesurface of LIG.

FIGS. 19A-19L are TEM images of LIG made under different gas atmosphere.2% laser duty cycle is used for these samples. (FIGS. 19A-19F) Scalebars: 200 nm. (FIGS. 19G-19L) Scale bars: 20 nm.

FIGS. 20A-20B are film of LIG that was scraped from the PI surface andprepared through vacuum filtration. This LIG was made with air assist.FIG. 20A is a top view SEM image of the filtered LIG film. FIG. 20B isan image of water droplet on the filtered LIG film; the measured contactangle is ˜120°.

FIG. 21A is a scheme of different laser rastering directions (methods2101 and 2102) provide different wetting properties. The picture 2103shows a water droplet sitting on the hydrophobic LIG surface from method2102, the measured contact angle is 143°.

FIGS. 21B-121C are SEM images of hydrophilic LIG which has few carbonnanoparticles (method 2101).

FIGS. 21D-21E are SEM images of hydrophobic LIG which are coated withcarbon nanoparticles (method 2102). All fabrications of LIG with gasassist disclosed herein used method 2101.

FIGS. 22A-22B are (FIG. 22A) C 1s and (FIG. 22B) O 1s peaks of LIG madewith H₂ in the chamber with different laser powers.

FIG. 22C shows the relationship between contact angle (bars), O content(red dots), and C—O bond content (of total O content, blue circles) forLIG samples made with H₂ in the chamber with different laser dutycycles.

FIG. 22D-22E are (FIG. 22D) C 1s and (FIG. 22E) O 1s peaks of LIG madewith Ar in the chamber with different laser duty cycles.

FIG. 22F shows the relationship between contact angle, O content, andC—O bond content (of total O content) for LIG samples made with Ar inthe chamber with different laser duty cycles. The error bars reflect thedifference between various spots of the same sample.

FIG. 23 shows the relationship between captive bubble contact angle(bars), O content (red dots), and C—O bond content (of total O content,blue circles) for LIG samples made under different gas atmospheres. 2%laser duty cycle is used for these samples. C—O peak assigned at 533.4eV, C═O peak assigned at 532.3 eV for the calculation of C—O content.The error bars reflect the difference between various spots of the samesample.

FIG. 24A is a side view SEM image of LIG made with SF₆ in the chamber.

FIG. 24B is the depth profile of C/O/F content (black, red and bluedots, respectively) of LIG made with SF₆. An Argon ion beam is used toetch the LIG surface, the estimated etch rate is ˜20 nm/min.

FIGS. 24C-24D are (FIG. 24C) C 1s and (FIG. 24D) F 1s spectra of LIGmade with SF₆ with different etch times. A 9.3 μm CO₂ laser was usedwhen SF₆ was present. 4% laser duty cycle is used for this sample.

FIG. 25 shows the relationship between contact angle (bars) and C/F/O/Ncontent (red dots, blue dots, blue cycles, blue triangles, respectively)for LIG samples made with SF₆ in the chamber with different laser dutycycles. A 9.3 μm CO₂ laser was used when SF₆ was present. The error barsreflect the difference between various spots of the same sample.

FIGS. 26A-26C show SEM and TEM images of LIG prepared with SF₆(chamber). A 9.3 μm CO₂ laser was used when SF₆ was present. 4% laserduty cycle is used for this sample.

FIG. 27 shows stability of the superhydrophilic/superhydrophobic LIGsamples. Contact angles are measured as prepared, after one week inambient air, and after one year in ambient air.

FIGS. 28A-28F are (FIG. 28A-28C) advancing and (FIG. 28D-28F) recedingcontact angles of LIG with Ar, H₂, and SF₆, respectively. The values are159°/147°, 160°/156°, and 164°/159°, respectively. 2% laser duty cycleis used for LIG samples prepared with Ar and H₂ (chamber). A 9.3 μm CO₂laser was used when SF₆ was present, and 4% laser duty cycle is used forLIG samples prepared with SF₆ (chamber).

FIGS. 29A-29B are top-view SEM image of LIG filter.

FIG. 29C is a water droplet on the surface of the LIG filter, themeasured contact angle is 155°.

FIGS. 29D-29F are filtration of CHCl₃/H₂O mixture with the LIG filter. ACHCl₃-soluble blue dye is used for oil phase visualization. (FIG. 29D)Water does not go through the filter; (FIG. 29E) CHCl₃ goes through thefilter; (FIG. 29F) water stays on top of the filter even after all ofthe CHCl₃ went through.

FIGS. 30A-30F show the anti-icing properties of LIG. FIG. 30A shows aLIG sample (made in air) tilted 45° at a temperature of −15 to −20° C.FIG. 30B shows water (˜0° C.) dripped onto the LIG sample in FIG. 30A.FIG. 30C shows ice formed on LIG sample in FIG. 30B after 1 min. FIGS.30D-30F show the same process as with FIGS. 30A-30C but using a LIGsample made in Ar (chamber); ice only formed on PI but not on LIG. 2%laser duty cycle is used for these samples.

FIGS. 31A-31B show the specific capacitances of supercapacitors madefrom LIG samples made with O₂ in the chamber (different laser dutycycles) and with air (2% laser duty cycle). The X % in the label in FIG.31A stands for the laser duty cycle of LIG samples made with O₂ in thechamber. “Air1” stands for air assist, “Air2” stands for air in thechamber.

FIG. 32 shows the water droplet appearance on the LIG surface preparedwith N₂ in the chamber using 2% laser duty cycle. The measured contactangle is 153°.

FIG. 33 shows the Raman spectrum of polyetherimide lased with a 10.6 μm.The increased graphene composition with multiple laser exposures (notedby the number of lases then x in the inset) is evident from the increasein the G peak in the Raman spectrum at −1580 cm⁻¹.

FIG. 34A is a schematic of PSU class polymers LIG via laser induction.

FIG. 34B is A photo of LIG patterned on PSU, PES and PPSU polymers(inset show an example of the flexibility of PPSU-LIG).

FIGS. 34C-34E are, respectively, is XRD, Raman spectrum, and XPS surveyof PSU-, PES- and PPSU-LIG.

FIGS. 35A-35L are SEM and TEM images for PSU-class LIG. FIGS. 35A-35Care SEM images of PSU-LIG at (a) low resolution; (b) high resolution;and (c) cross-section; respedtively. FIG. 35D is a TEM images forPSU-LIG. FIGS. 35E-35G are SEM images of PES-LIG at (e) low resolution;(f) high resolution; and (g) cross-section, respectively. FIG. 35H is aTEM image for PES-LIG. FIGS. 35I-35K are SEM images of PPSU-LIG at (i)low resolution; (j) high resolution; and (k) cross-section,respectively. FIG. 35L is a TEM image for PPSU-LIG.

FIGS. 36A-36I are high-resolution XPS spectra de-convolution of PSU-,PES- and PPSU-LIG and the corresponding polymer substrate. C1sde-convolution for (FIG. 36A) PSU-LIG; (FIG. 36B) PES-LIG; and (FIG.36C) PPSU-LIG. S2p de-convolution for (FIG. 36D) PSU-LIG; (FIG. 36E)PES-LIG; and (FIG. 36F) PPSU-LIG. S2p de-convolution for polymersubstrates (FIG. 36G) PSU; (FIG. 36H) PES; and (FIG. 36I) PPSU.

FIGS. 37A-37F show hydrogen peroxide generation at 1.5-2.5 V withdifferent PSU-class LIG as electrodes. Using aqueous NaCl (0.05 M) (FIG.37A) PSU-LIG; (FIG. 37C) PES-LIG; and (FIG. 37E) PPSU-LIG. Using aqueousNa₂SO₄ (0.05 M) (FIG. 37B) PSU-LIG; (FIG. 37D) PES-LIG; and (FIG. 37F)PPSU-LIG.

FIG. 38 reflects biofilm growth on graphite, polymer film substrates,and LIG showing average thickness and biomass. Representative IMARISsoftware images are shown above. These images show live and deadbacteria and extracellular polymeric substances (EPS). Scale bars: 100μm.

FIGS. 39A-39F show inhibition of P. aeruginosa (˜10⁶ CFU mL⁻¹) atdifferent voltages (0-2.5 V) expressed as % inhibition or bacterial logreduction by different PSU-class LIG electrodes with (FIGS. 39A-39B)PSU-LIG; (FIGS. 39C-39D) PES-LIG; and (FIGS. 39E-39F) PPSU-LIG.

FIG. 40A is an illustration of LIG printed on the commercial UP150 PESporous membrane, including a photograph of the UP150-LIG membranecoupon.

FIG. 40B are SEM images of the UP150-LIG filter at differentresolutions.

FIG. 40C is a Raman spectra of UP150 membrane substrate and UP150-LIG.

FIG. 40D is a mixed bacterial solution (10⁻⁶ CFU mL-1) that was passedthrough commercial and self-made membranes (PES 1 and PES 2) coated withLIG.

FIG. 40E is a calculated biofilm biomass and average thickness on UP150membranes and UP150-LIG. Representative IMARIS software images are shownabove. These images show live and dead bacteria and EPS. Scale bar: 100mm.

FIG. 40F is an illustration of stacked LIG-filter electrodes.

FIG. 40G is a filtration of bacterial solution (˜10⁶ CFU mL-1) at 2.5 Vand ˜500 L m⁻² h⁻¹ with different commercial LIG-filters. The insetshows the UP-150 LIG filter at different voltages at an ultra-high flowrate (˜22000 L m⁻² h⁻¹).

FIG. 41 is an embodiment of a simple implementation of 3D printing ofgraphene using a thermoplastic polymer powder (polyphenylene sulfide).In this case, all cross sections are squares resulting in a cuboid 3Dstructure.

FIG. 42A is TEM image of activated carbon.

FIG. 42B is TEM image of laser-induced graphene obtained from activatedcarbon.

FIG. 43 is a Raman spectra of a polyphenlyene sulfide-activated carbon(PPS-AC) mixture that has been printed into a 3D structure by exposureto 10.6 micrometer CO₂ laser at 5% laser power 5% speed.

FIG. 44A is a photograph of a 5 mm³ 3D graphene monolith printed fromPPS-AC using a powder bed printing method.

FIG. 44B is an SEM image of corner of the cube shown in FIG. 44A at 50×magnification (scale bar is 1 mm).

FIG. 44C is an SEM image of the surface of the cube shown in FIG. 44A(scale bar is 50 μ.m).

FIGS. 45A-45C are photographs of freestanding graphene objects printedusing a 50/50 mixture of polyphenylene sulfide and activated carbon withfeatures less than 1 mm in width (scale bar is 1 cm).

FIG. 45D is a Raman spectra of a PPS-AC graphene object.

FIG. 46A is a schematic of 3D printing box.

FIG. 46B is a photograph of a powder bed box.

FIGS. 47A-47B are schematics of a 3D printing box in a controlledatmosphere chamber.

FIGS. 47C-47E are photographs of a 3D printing box in a controlledatmosphere chamber with a ZnSe window.

DETAILED DESCRIPTION

The present invention expands the range of properties for LIG,especially to tune the hydrophobicity of the LIG surface, and furtherextends the field of applications for LIG based on such differentproperties.

Laser-Induced Graphene by Multiple Lasing

The present invention is directed to a method of using multiplepulsed-laser scribing to convert a wide range of substrates intolaser-induced graphene (LIG), i.e., a simple and facile method ofobtaining patterned graphene on the surface of diverse materials rangingfrom natural, renewable precursors (such as cloth and paper) tohigh-performance polymers (such as Kevlar).

With the increased versatility of the multiple lase process, highlyconductive patterns can be achieved on the surface of a diverse numberof substrates in ambient atmosphere. The use of a defocus method ofobtaining multiple lases in a single pass of the laser allows for thismethod to be implemented without significantly increasing processingtimes as compared with laser induction of graphene on polyimide (Kapton)substrates previously reported. In fact, any carbon precursor that canbe converted to amorphous carbon can be converted to graphene using thismultiple lase method including, for example, burnt toast. A generallyapplicable technique for forming graphene on diverse substrates opensthe possibility for many applications such as flexible and perhaps evenbiodegradable and edible electronics.

FIG. 1A depicts the conversion of a coconut surface into LIG in theshape of the letter “R.” The surface of a coconut was converted into a3D porous graphene structure by irradiation with a 10.6 mm CO₂ laserunder ambient atmosphere.

Such fabrication of LIG by multiple lasing occurred as follows: AnXLS10MWH (Universal Laser Systems) laser platform was used to induce theformation of graphene on the various tested substrates. The XLS10MWH wasequipped with a 10.6 μm CO₂ pulsed laser (75 W) and a 9.3 μm CO₂ pulsedlaser (50 W) and a 1.06 μm fiber laser was used to perform the laserinduction for all materials. An image density of 1000 DPI and typicallya scan rate of 15 cm/s was used but differing scan speeds were used.Generally, a laser duty cycle of 1-5% was used during the fabrication ofLIG depending on the substrate used. Laser duty cycle refers to thepercentage of time that the laser is active yielding an average powerover the duration of each laser spot. The computer software supplied ULSadjusted the pulse widths and quiet times to achieve the desired averagepower. The laser was focused by lasing commercial PI (Kapton, thickness127 μm, McMaster-Carr) at various z-axis heights and zeroing at thesetting yielding the smallest LIG spot sizes. Z-axis defocus is inrelation to this reference point.

The lignin-containing precursor material can be easily patterned withLIG by computer-controlled laser rastering over the surface. Areasexposed to the laser light were converted by a photothermal process tographene whereas areas not exposed to the laser remain unchanged. Thepresence of graphene was evidenced by the Raman spectrum depicted inFIG. 1B. FIG. 1C shows the transmission electron microscopy (TEM) imageof a coconut-derived LIG flake. Higher resolution TEM images showed thatthe flake consists of few-layer graphene that reveal clear graphenefringes with the characteristic 0.34 nm d-spacing.

The coconut shell was exposed to a 75 W laser with power setting rangingfrom 5-10% power. It was found that a single exposure of the coconutshell using 5% power resulted in the formation of amorphous carbon. SeeFIGS. 2A-2B. Repeated lasing of the same portion of the substrate (up to5×) resulted the graphene observed in FIG. 1D. Similar results wereobtained for cork and potato skins (FIGS. 1E-1F, respectively) asdetermined by Raman microscopy.

This reflects that in some cases the mechanism of LIG formation involvedthe conversion of a carbon precursor first to amorphous carbon followedby a conversion to graphene upon subsequent lasing. FIG. 3 is an IRspectrum of amorphous carbon (curve 301) and laser-induced graphene(curve 302) derived from cork. The locations of the 10.6 μm and 9.3 μmbands of a CO₂ laser are denoted by the vertical line 303 and 304,respectively. As depicted in FIG. 3, amorphous carbon absorbs stronglyin a range from ˜500-1500 cm⁻¹ Amorphous carbon can be considered aheterogenous material consisting of sp² carbon clusters that areembedded within a sp³ matrix [Ferrari 2003]. CO₂ lasers output a bandcentered at 10.6 μm but ranges between 927-951 cm⁻¹ [Patal 1964]. Thesefrequencies are absorbed by the C—C and C—H bonds present in theprecursor substrate materials that are not present in LIG. See FIG. 3.

As such, it is likely that the substrate is first photothermallyconverted to amorphous carbon. Subsequent exposures of the amorphouscarbon then effect the transformation of the amorphous carbon tographene. This selective breaking of non-aromatic bonds is potentiallyone reason why mere thermal treatments or irradiation with otherwavelengths upon carbon only resulted in amorphous carbon. For example,lasing of polyimide film with an ultraviolet laser (275-363 nm) waspreviously reported to only result in amorphous or glassy carbon despiterepeated lasing (up to 35 times) [Srinivasan 1995; Srinivasan 1994].Clearly, the wavelength of the laser irradiation matters for obtaininggraphene by multiple lasing. More recently, polyimide was ablated with a308 XeCl excimer laser and the carbon material was characterized after200-800 pulses but no graphene-based 2D Raman peaks were detected[Raimondi 2000]. By contrast, only 3-5 passes of a rastered CO₂ laseryields porous graphene from a wide variety of substrates. As such, boththe wavelength of the laser irradiation as well as the number ofexposures is important to the formation of LIG.

To further confirm, activated carbon was irradiated with multipleexposures to a pulsed 75 W 10.6 mm laser at 5% power at a 15 cm/s scanrate. Both TEM and Raman characterization show that amorphous carbonpowder can be converted to LIG by multiple lasing. See FIGS. 4A-4C. Thisresult demonstrates that the multiple lasing process for making grapheneis generally applicable to any material that can be first converted to alayer of amorphous carbon. As such, multiple lasing can be used todirectly obtain graphene from many substrates in a one-step process bylaser irradiation but can also be applied to thermally and chemicallycarbonized materials. Moreover, inexpensive carbon sources, such asactivated carbon, can now be used in the preparation of graphene whichmay have implications in commercial applications for LIG.

Two methods were used to obtain multiple lases of a substrate. The firstmethod involved multiple passes of the rastered laser. At 5% power ofthe 75 W laser, the spot size of the laser was ˜175 mm in diameter.Given that the samples were lased using the 1000 dots per inch (DPI, asetting on commercial laser systems; 1 inch is 2.54 cm) raster density,multiple exposures occurred naturally with the overlap of the laserspots. For a 175 μm diameter spot size, each location at which thesubstrate was exposed has ˜37 overlapping laser spots. Multiple passesof the laser would result in an additional 37 lases per pass.

A second method for obtaining additional exposures was developedinvolving increasing the spot size of the laser while keeping thedensity of the dots consistent (1000 DPI). Referring to FIG. 5A, thiswas achieved by defocusing the laser 501 to take advantage of the factthat the shape of the focused laser beam is conical. By altering thez-axis distance from the focal plane 502 (such as planes 503 and 504 at−1 mm and −2 mm, respectively, different spot sizes can be obtained. Forprecursor material 505, located at the focal place 502, the areasexposed to the laser are shown in the circles 506. For precursormaterial 507, located at the focal place 504, the areas exposed to thelaser are shown in the circles 508. For instance, lowering the substrateby ˜1.02 mm results in the increase of the spot size from 175 mm to 300mm in diameter. This results in effectively 3 times more lases in anygiven location of the substrate being lased since the area of each spotincreases but the density of laser spots remains constant. FIG. 5B is agraph that shows the effective number of lases as a function of thez-axis defocus. The advantage of this method is the increase inprocessing speed as each spot can be lased many additional times in eachpass of the laser. A combination of defocus and multiple laser passescan be used to lase a material the desired number of times.

This technique was applied to ULTEM polyetherimide (PEI) which hadpreviously been found to perform much more poorly than PI as an LIGprecursor substrate [Lin 2014]. The PEI was lased at various defocusranging from 0 (at focal plane) to ˜2 mm defocus at 5% power and a scanrate of 30 cm/s. Even with no defocus, Raman spectroscopy in FIG. 6Ashowed the presence of graphitic carbon with a broad D peak observed at˜1350 cm⁻¹ and a 2D peak near 2700 cm⁻¹. Using a defocus of ˜0.75-1.25mm, significant improvements in the I_(D)/I_(G) ratios were observed inFIG. 6C. As shown previously, a ˜0.75 mm defocus is equivalent to lasingthe substrate ˜2.7 times. Moreover, as shown in FIG. 6D, thefull-width-at-half-maximum (FWHM) of the G peak is narrowest at the samedefocus. Consistent with these indications of better quality graphene,the LIG showed the lowest sheet resistance (˜15 ohms/sq) at ˜0.75 mmdefocus as determined by 4-point probe measurements. To confirm, PEI wasalso lased without defocusing (1% power and 30 cm/s scan rate) up tofour times. The sheet resistance was found to be lowest after 3 lases.By contrast, even though the overall fluence is higher, lasing a singletime at 5% power and the same speed yields LIG with a worse I_(D)/I_(G)ratio compared with multiple lased LIG. The sheet resistance was alsohigher at ˜65 ohm/sq, which is substantially worse than the multiplelased materials whether by multiple raster or by defocusing the beam.This showed that the improvement in the quality of the graphene arisesfrom application of multiple lases rather than just total fluence oflaser energy to the substrate.

Having developed a method for improving the quality of the LIG bymultiple lasing, this method was tested on numerous substrates thatpreviously did not yield laser-induced graphene when lased at the focalplane. Using a combination of the multiple raster and defocus methods ofmultiple lasing, it was found that a wide range of polymers could beconverted to LIG, as reflected in TABLE 1 (with T_(g) and T_(m) are theglass transition temperature and melting temperature, respectively).

TABLE 1 T_(g)/T_(m) (□) Trade Name High-Temperature ThermoplasticsPoly(m-phenylenediamine) isopthalamide 225/380 Nomex Polyimide (PI) 280Kapton Polyamide Imide (PAI) 277 Torlon Polyether Imide (PEI) 215 UltemPolyphenylene Sulfone (PPSU) 225 Radel PPSU Poly-parapheyleneterphthalamide Kevlar Polybenzimidazole (PBI) 427 Polyether Ether Ketone(PEEK) 143/334 Polyphenylene Sulfide (PPS)  85/285 Chlorinated polyvinylchloride (CPVC) Thermoset Materials Polystyrene (crosslinked) 114/640Rexolite Epoxy Varies (up to 350) Phenolic Resin 300/570 BakeliteNatural Polymer Materials Lignin Varies Cellulose (phosphate treated)300-350 Non-Polymeric Materials Activated Carbon Charcoal AnthraciteCoal

High temperature polymers with higher melting points and crosslinkedthermoset plastics tended to perform better for direct laser conversioninto LIG. TABLE 1 shows a list of polymers that can be directlyconverted to LIG by lasing in air. These obtained LIG materials showedthe characteristic 2D peak in their respective Raman spectra. Laserirradiation under N₂ atmosphere was performed in a sealed chamber with aZnSe window.

Since applicants now have discovered that the mechanism of LIG formationdoes not require a one-step conversion of a precursor into LIG, itallows for the development of additional methods of obtaining LIG. Infact, the multiple lase technique is applicable to any carbon precursorthat can be converted to amorphous carbon. For example, LIG was obtainedby a 1 mm defocused exposure of a piece of bread that was firstcarbonized in a toaster oven.

This technique was applied to materials that were predominantlycellulose that previously could not be converted directly tolaser-induced graphene either in ambient air or in a N₂ atmosphere.Carbohydrates, such as cellulose and starch, decompose into levoglucosanwhich then further decomposes into volatile compounds [Kandola 1996].Fortunately, methods for increasing the char yield of cotton-basedmaterials have previously been thoroughly investigated. [Id.] Whatmanfilter paper, cloth, and other cellulose-based materials were thentreated with a commercial organic phosphate salt containing fireretardant or ammonium polyphosphate. The materials were then exposed toa propane torch to char the surface of the material and to obtainamorphous carbon. Exposure to the 10.6 μm laser then converted amorphouscarbon to LIG. FIGS. 7A-7C. show optical images of the filter paperbefore charring over an open flame, after charring, and after lasing,respectively. Raman showed that charred filter paper consisted ofamorphous carbon but a single lase with the CO₂ laser was sufficient toconvert the material to LIG. XPS showed that the elemental compositionof the LIG changes with subsequent multiple lasing. Charred filter paperstarted out at ˜55% carbon and 35% oxygen with <5% of phosphorus andnitrogen. Subsequent lasing caused the carbon content of the LIG toincrease to nearly 80%.

It was subsequently found that directly lasing of cellulose containingmaterials such as cloth, cotton paper, and filter paper could beachieved without thermally charring the material in advance albeit withlower quality graphene as determined by conductivity measurements andthe Raman spectra of the obtained LIG. See FIGS. 8A-8D. With thismethod, any material that can be converted to amorphous carbon canfurther treated by CO₂ laser to obtain graphene. This enables a generalmethod of obtaining LIG from carbon precursors.

The lignocellulosic structure of wood with high lignin content could beconverted into LIG by irradiation under inert or reducing atmosphere.The need for a carefully controlled atmosphere is obviated usingfire-retardant treatment to promote the formation of carbon char bycatalyzing the dehydration during lasing. Commercially produced fireretardant-treated plywood (D-Blaze) was lased in ambient atmosphere andLIG was obtained. Ablation was observed when the wood was exposed to 10%speed 5% power laser irradiation at the focal point but extremelyconductive LIG (˜8 Ω/sq) was obtained when the defocus was increased to˜1 mm. In addition to cellulose, other polysaccharides can be convertedto LIG if first treated with fire retardants. For example, bread wastreated with commercial “Fire Guard” phosphate based fire retardant wasallowed to dry in air. Subsequent lasing converted the surface of thebread into a conductive surface consisting of LIG. See FIGS. 9A-9D.Direct conversion of wood and wood products, such as paper to graphene,in ambient atmosphere will likely have significant commercialimplications since conductive patterns can be produced without requiringvacuum chamber. Indeed, the multiple lase method allows for the eitherthe direct conversion of polymeric carbon precursors to LIG or even anymaterial that can be first converted to amorphous carbon.

In short, multiple lasing allows almost any carbon precursor that doesnot ablate when exposed to a CO₂ laser to be converted into LIG.High-temperature engineering plastics such as Kapton, Kevlar,polysulfones, polyetherimide, polyphenylene sulfide, among others arereadily converted into LIG. Cross-linked polymers such as phenolic resinand crosslinked polystyrene are also suitable substrates for LIGformation. While lignin is the only natural polymer that can beconverted to directly LIG, polysaccharides such as cellulose and starchcan be readily activated for conversion to LIG with the application ofboric acid or phosphate-based fire retardants. See FIGS. 9A-9D. The easeof obtaining a porous graphene surface on biodegradable substrates suchas wood, paper, coconuts, potatoes, cardboard, and cloth as well as theexcellent conductivity (<5 ohms/sq sheet resistance) will potentiallyallow for many electronic applications such as supercapacitors, wiring,batteries, transistors, RFID antennae, sensors and other applications.

Utility and Variations

A general method of converting carbon precursor materials into graphenecould be exceptionally useful given the properties of graphene. Beingable to pattern conductive layers of LIG on a variety of materials wouldpotentially allow for applications such as supercapacitors, watersplitting catalysts, sensors, flexible electronics, and otherapplications. Conductive graphene traces on cotton clothing for examplecould potentially be useful for wearable electronics. The same LIG oncotton cloth might be useful for water purification applications.Additional potential applications of laser-induced graphene can be foundin the Tour '821 application.

As compared with the previous methods, this method of forming LIG isparticularly useful because it enables the use of natural, abundant, andrenewable sources of carbon, such as wood, paper, cloth, and any othermaterial to form LIG. Non-polymeric sources of carbon can also be usedwith this method, which was not the case for the previously reportedmethods. For example, sugars can be charred into a layer of amorphouscarbon and then converted into LIG by multiple lases. Or, for example,activated charcoal or biochar can be converted to conductive LIG.

The improved method of generating laser-induced graphene can thus beapplied generally and not only to certain expensive high temperaturearomatic plastics.

Specifically, the prior art only described the tuning of laserparameters to match a polymer substrate. By contrast, the methods of thepresent invention involve multiple lases of a precursor to obtainlaser-induced graphene. The prior art limited the claim of LIG tomaterials derived from the lasing of a polymer precursor. By contrast,most materials that can form a layer of carbon on the surface can beconverted into laser-induced graphene by the method described. Theinitial conversion of the surface of the material into a layer of carbonneed not be by laser exposure but can be performed by thermal (burningwith a flame) or chemical methods.

Many materials tend to vaporize and ablate away when exposed to highenergy lasers. This ablation means that the carbon contained in theprecursor would be lost without the opportunity for it to rearrange intographene. Additionally, oxygen (if present) may oxidize the materialresulting in the precursor burning away rather than yielding anappreciable yield of the laser-induced graphene. Methods of addressingthis for certain carbon-containing precursors include the following:

Control Over Reaction Atmosphere—

Inert or reducing atmospheres combined with variation of gas pressurescan reduce oxidation and vaporization of precursor materials. See R. Yeet al. “Laser-Induced Graphene Formation on Wood”, Adv. Mater. 2017,29(37), 1702211 and supporting information, which are herebyincorporated by reference in their entirety for all purposes.

Carbon precursors for LIG can be inserted into a closed chamber with awindow that is transparent to laser irradiation of the selectedwavelength. For example, ZnSe can be used as a transparent windowmaterial with a 9.3 or 10.6 μm laser. The chamber can then be placedunder vacuum, purged, and filled with an inert gas such as Ar or N₂after which the material is exposed to laser irradiation. Alternativelya reducing atmosphere such as H₂ can also be used.

Pre-Carbonization—

Converting the surface of a precursor material into amorphous orgraphitic carbons by thermal or chemical means. For example wood can beconverted to charcoal in a flame which does not vaporize as readily whenexposed to laser irradiation.

Char Promoting Catalysts—

Catalysts can be applied to some materials to promote the formation ofamorphous or graphitic carbons on the surface of some materials thatwould otherwise tend to vaporize.

Thus, with the methods of the present invention, carbon precursors otherthan the previously reported polyimide (PI) and polyetherimide (PEI) canbe converted into laser-induced graphene materials, such as variousaromatic polymers, lignin-containing materials, cellulose-basedmaterials, and non-polymeric sources of carbon.

Some of the aromatic polymers that have been converted to laser-inducedgraphene by this method include polymers such as polyphenylene sulfide,polyamide-imide, polybenzimidazole, phenol-formaldehyde resin,poly(ether ether ketone) (PEEK), poly(ether sulfone),poly(m-pheylenediamine) isopthalamide, crosslinked polystyrene, epoxy,and poly(ether-imide). Lignin-containing materials include wood, coconutshells, potato skins, and burlap (jute fibers). Cellulose-basedmaterials to promote LIG formation include cotton cloth, paper,cardboard (including those that are catalyst treated). Non-polymericsources of carbon include amorphous carbon, charcoal, biochar, activatedcarbon, coal, asphalt, coke, and Gilsonite. Each of these can beemployed to obtain LIG using the method of the present invention.

Previously, studies showed that only polymers containing aromatic andimide structures were reliably converted to porous graphene by laserscribing. The present invention is a laser scribing method for theproduction of graphene that can be generally applied to most carbonprecursors. The method of the present invention also applies tonon-polymeric materials, such as amorphous carbons, biochar, activatedcarbon, activated charcoal, coal and most other carbon sources.

Typically, in order to use a cellulose-based materials in the presentinvention, such as paper, it is advantageous to pre-treat such materialswith a flame retardant. For example, a phosphate-based or borate-basedflame retardant can be utilized. Alternative, the surface of thecelluylose-based material, such as paper, can be charred beforehand.

Metal Solutions.

It has further been shown that one or more metal salt solutions, metaloxide solutions, or metal nanoparticle solutions can be added to thelaser-induced graphene and then lased again. In this way, the metalnanoparticles or the metal salts (after reduction by the lasing process)or metal oxides (with or without subsequent reduction) form metalnanoparticles or metal carbide nanoparticles or metal oxidenanoparticles that are dispersed in the laser-induced graphene. TheseLIG-dispersed nanoparticles can act as catalysts for reactions, and morespecifically organic oxidation or reduction transformations, orelectrocatalytic transformations such as hydrogen evolution reactions(HER), oxygen evolution reactions (OER), hydrogen oxidation reactions(HOR) and oxygen reduction reactions (ORR). HER and OER are importantfor water splitting to make hydrogen gas and oxygen, and HOR and ORR areimportant for fuel cell chemistry.

Metal nanoparticles and metal salts or metal oxides that can be usedinclude Co, Ni, Pt, Pd, Fe, Ru, and more generally transition metals orcombinations thereof, or mixtures of transition metals and main groupelements such as chalcogenides or phosphides, the metal phosphides, suchas cobalt phosphides or nickel phosphides being particularly active aselectrocatalysts.

Roll-to-Roll Process.

Furthermore, the material can be used in the form of a roll so that aroll-to-roll process can be employed. Generally paper is the leastexpensive material that can be utilized in roll form. Other materialsthat can be utilized in roll form include cardboard and polymer films.

Dopants.

Variations further include modifications, such as the addition ofdopants, that can be used to improve the performance of thelaser-induced graphene for additional applications. Heteroatoms such asboron and phosphorous can be introduced by addition of compoundscontaining those elements to the carbon precursor. Metals, metal oxides,metal chalcogenides, metal nanoparticles, salts, organic additives, andinorganic additives can all be added to modify the properties of theobtained graphene such that the graphene is suitable for variouselectronic and catalytic applications.

Fabrication of Laser-Induced Graphene in Controlled Atmospheres

The present invention further includes a method to fabricate LIGstructures under controlled gas atmospheres, where superhydrophilic,highly hydrophilic, highly hydrophobic, and superhydrophobic LIG areobtained by changing the gas environment. A material is“superhydrophilic” when the water contact angle of the material is lessthan or equal to 1°, and a material is “highly hydrophilic” when thewater contact angle is between 1° and 10°. A material is“superhydrophobic” when the water contact angle of the material is morethan or equal to 150°, and a material is “highly hydrophobic” when thewater contact angle is between 135° and 150°.

In some embodiments, a controlled atmosphere chamber (that washome-made) allowed gas to controllably flow through the chamber, while aZnSe window on top of the chamber permitted the CO₂ laser beam toirradiate the PI film that resided within the chamber. The gases studiedinclude O₂, air, Ar, H₂, and SF₆. LIG structures with differentproperties were obtained. This change in gas atmosphere permits anenormous change in the water contact angle on the as-prepared LIG, from0° (superhydrophilic) when using O₂ or air, to >150° (superhydrophobic)when using Ar or H₂. F-doping of the LIG was also demonstrated under aSF₆ gas atmosphere, where an even higher contact angle (>160°) could bereached due to the low surface free energy of the C—F bonds. Scanningelectron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), andRaman spectroscopy showed that the different wetting properties are dueto the LIG surface morphology and the edge and surface chemistry ofthese LIG structures. While superhydrophobicity can be introduced withAr, H₂, or SF₆ in the controlled atmosphere chamber, LIG samplesfabricated under O₂ flow show an increased number of defects thatproduce a significantly improved specific capacitance (compared to LIGmade in air) when the LIG was used as the electrode material formicrosupercapacitors, showing the versatility of the controlledatmosphere chamber fabrication method.

The schemes for the fabrication of LIG structures under controlled gasatmosphere are shown in FIGS. 10A-10C. Generally, a 10.6 μm CO₂ laser isused to directly convert PI into LIG structures with different gasatmosphere control methods. For the gas assist method (FIG. 10A), anozzle is used to blow the selected gas directly at the laser spot,while the sample is still surrounded by air. In this case, onlynon-flammable gases (or gas mixtures below their explosion limit) wereused due to safety concerns, but it is not essential as long as air oroxygen is not present. For instance, inventors of the present inventionselected air and 3% H₂ in Ar to explore both oxidizing and reducing orinert gas assist. For the controlled atmosphere chamber method (FIGS.10B-10D), different gases have been introduced through the gas line;this fabrication process mimics the traditional CVD process for graphenegrowth and modification [Mattevi 2011], but replaces the extendedhigh-temperature heating with laser irradiation. Due to the isolationfrom air, a larger range of gas environments were tested with thecontrolled atmosphere chamber method, including O₂, air, Ar, and H₂, anda significant change in LIG properties was observed in terms ofhydrophilicity and hydrophobicity. Details for the fabrication of LIGsamples under different gas atmospheres are discussed below.

FIGS. 10E-10J show the SEM images and contact angle measurements for LIGsamples prepared under various atmospheres. For samples prepared withair assist, 3% H₂/Ar assist, and air in the chamber, the LIG structuresshare a similar porous morphology with a mixture of sheet-like andstrip-like components [Lin 2014]; this similarity could come from thefact that even though 3% H₂/Ar assist was blown at the laser spot, theoverall environment still contains much air. For LIG with O₂ in thechamber, however, much rougher edges were observed, presumably resultingfrom the excess oxidation of the graphene structure. Rough edges werealso observed from LIG with H₂ in the chamber to create a hierarchicalnano-structure, as the irregular defects on graphene structures wereprotected from oxygen capping by the reducing environment. From thelower magnification SEM images (FIGS. 16A-16L), much more significantmacro-porous structures can be observed for LIG samples prepared withair assist and O₂ in the chamber, presumably caused by the strongoxidizing environment.

The higher-resolution SEM images show the rough edges for both samples(FIGS. 17A-17B). The degree of defects was analyzed by Ramanspectroscopy (vide infra). For LIG prepared with Ar in the chamber,aggregated carbon nanoparticles were also observed on the surface of theLIG flakes, especially from the additional TEM images shown in FIGS.18A-18B. These aggregated carbon nanoparticles are probably the productof the carbonization of the PI under the inert atmosphere, forming anenhanced hierarchical microstructure for the LIG sample made with Ar inthe chamber. Although certain morphology differences have been observedunder SEM for LIG samples prepared under the different atmospheres,there are common features such as the similar LIG thickness of ˜40 μm(FIGS. 16A-16L) and the randomly distributed graphene edges which wereobserved under TEM (FIGS. 19A-19L). [Lin 2014].

The inset images in FIGS. 10E-10J show the water contact angles for LIGsamples prepared under different gas atmospheres. Superhydrophobic(contact angle >150°) surfaces were obtained from reducing or inertenvironments, namely Ar in the chamber (152°) or H₂ in the chamber(157°), while all other samples prepared with the presence of O₂ showsuperhydrophilicity (˜0°).

Interestingly, while the as-prepared LIG surface made with air assist issuperhydrophilic, scratching off the LIG from the PI into a powder andmaking an LIG film by filtration, obtains a hydrophobic surface with acontact angle of ˜120°, as shown in FIGS. 20A-20B. This might underscorethe significance of the morphology, or surface orientation, of theas-prepared LIG surfaces.

For the as-prepared LIG sample on PI, the hydrophilic oxidized edgesmight be facing upward, making direct contact with water, while theporous surface permits the water droplet to penetrate into the LIGstructure. In the case of the LIG film prepared by removal andfiltration, the more hydrophobic graphene basal planes are exposed tothe water droplet [Wang 2009], retarding penetration of the waterdroplet. Conversely, it could be that only the upper surface of theas-prepared film is superhydrophilic, and the removed LIG exposes thehydrophobic lower portions.

In another interesting and controllable protocol, if one changes thelaser rastering direction relative to the gas assist direction duringLIG fabrication, carbon nanoparticles generated under laser irradiationare blown back onto the previously formed LIG surface instead of beingblown away (the normal setup), as shown in FIGS. 21A-21E. In this case,hydrophobic surfaces are obtained affording a contact angle of 143°.Here, the hydrophobic surface properties apparently come from theenhanced hierarchical structure created by the carbon nanoparticles, afrequently reported phenomenon that can even generate superhydrophobicsurfaces. [Lee 2007; Bhushan 2009; Bhushan 2010]. Taken together,surface morphology significantly impacts the hydrophobicity of the LIGsamples, more specifically, the superhydrophilic as-prepared LIG (airassist) surface with exposed graphene edges, the hydrophobic film(filtered LIG powders, FIG. 20A-20B) with the exposed graphene basalplanes, and the hydrophobic as-prepared LIG (reversed air assist) withhierarchical structure covered by the carbon nanoparticles all presentdifferent surfaces to the applied water.

FIG. 11 shows a statistical summary of the water contact angles of LIGsamples prepared under different gas atmospheres. Even with differentlaser duty cycles, except for LIG prepared with Ar or H₂ in the chamber,almost all other samples show superhydrophilicity with ˜0° contact angle(except for 0.5% duty cycle with 3% H₂/Ar assist). For LIG made with Arin the chamber, superhydrophobicity is produced and the contact anglesremain relative constant (˜152°) with different laser duty cycles. ForLIG made with H₂ in the chamber, superhydrophobicity with a largervariance is observed, and 2% laser duty cycle gives the highest contactangle of 157°. It was concluded that as H₂ is much more reactive(reducing) than Ar (inert), when the laser irradiation conditionchanges, there will also be a larger response or change regarding theproperties of LIG structures; this topic will be further discussed belowespecially in terms of the changes in O content.

To further demonstrate the different wetting properties of various LIGsamples, a first video was taken (available athttps://www.youtube.com/watch?v=_xFBDkQH7GA) that showed asuperhydrophilic LIG surface patterned inside a superhydrophobic LIGframe, and water rolls off the superhydrophobic LIG surface but istrapped at the superhydrophilic LIG surface domains.

FIGS. 12A-12B show the XPS spectra for LIG samples made under differentgas atmospheres. From the C 1s spectra shown in FIG. 12A, the graphiticC peak (284.5 eV) is observed as the major component for all LIG samplesand is used to calibrate the XPS peak position. [Lin 2014]. LIG madewith air assist or 3% H₂/Ar assist shows obvious shoulder peaks at 286to 290 eV, corresponding to C—O/C═O bonds. [Hontoria-Lucas 1995; Marcano2010]. For the O 1s spectra, different peak heights (normalized with C1s peak) are observed for different LIG samples in FIG. 12B, and the Ocontent as well as C—O content (relative to total O content, i.e. totalof C—O and C═O content) are quantified in FIG. 12C after deconvolution.Generally, LIG samples made with gas assist (not isolated from air)shows significantly higher O content relative to LIG samples made in thecontrolled atmosphere chamber. Samples with superhydrophobicity,specifically LIG made with Ar or H₂ in the chamber, show significantlylower O and C—O content compared to the hydrophilic samples. In thecontrolled atmosphere chamber, more oxidizing atmospheres yield higher Oand C—O content.

To further investigate the relationship between O content and watercontact angle, for LIG made with Ar or H₂ in the chamber, the data fordifferent laser duty cycles was also plotted in FIGS. 22A-22F. Clearly,the difference in surface chemistry does correlate to the difference incontact angle. LIG samples with lower O content and lower C—O contentalmost always have a higher water contact angle. This trend holdsdespite the fact that the changes in O content and contact angle aresmaller for LIG made with Ar (less reactive than H₂) in the chamber.This correlation is rationalized by the fact that C—O and C═O bonds aremore polar than C—C or C—H bonds, so that more O content means the edgesare more favorable to interact with water, and thus more hydrophilic. Inaddition, C—O bonds can terminate in H making it C—OH, therefore morehydrophilic than C═O bonds. This trend is also confirmed by using thecaptive bubble method to evaluate the contact angle for air (instead ofwater) and thus the difference in surface properties for thesuperhydrophilic LIG samples. [Zhang 1989].

Using this method, FIG. 23 shows that with the controlled atmospherechamber, LIG samples with a less oxidizing atmosphere (air), compared toO₂, gives lower O and C—O content, and thus a lower air contact angle of˜146°. The air bubble cannot even stay on the LIG made with O₂ in thechamber, indicating a much higher air contact angle, thus greaterhydrophilicity. As with the water contact angle measurements, thecaptive bubble contact angles (˜0°) for LIG samples prepared with Ar andH₂ in the chamber both afford superhydrophobic structures.

In summary, based on the experimental results discussed above, bothsurface morphology and surface chemistry could contribute to thehydrophilicity or hydrophobicity of the LIG surfaces. Specifically,superhydrophilic or hydrophobic LIG surfaces can be obtained by varyingthe morphology of LIG samples prepared with air assist, andsuperhydrophilic or superhydrophobic LIG surfaces can be obtained bytuning the O content with different gas atmospheres. However, bothfactors should be taken into consideration when synthesizingsuperhydrophobic or superhydrophilic LIG samples, since the changes insurface chemistry are often accompanied by changes in surfacemorphology. As shown in FIG. 10E-10J and FIGS. 16A-16L, superhydrophobicsurfaces with their lower O content LIG contains a hierarchicalstructure with rough edges (H₂ in chamber) or carbon nanoparticles (Arin chamber), and superhydrophilic surfaces with their higher O contentLIG contains more macro-pores (air assist and O₂ in chamber).

Raman spectroscopy is also used to study the degree of graphitizationand defect formation for various LIG samples under differentatmospheres. [Ferrari 2006; Pimenta 2007]. As shown in FIG. 12D, D, G,and 2D peaks are observed for the LIG samples, similar to the previouslyreported LIG. [Lin 2014]. FIG. 12E shows the quantified results of D/Gand 2D/G ratios as they are commonly used to analyzed the quality ofgraphitic structures. Among the samples analyzed, a similar 2D/G ratioof 0.6 to 0.7 is observed that indicates good graphitization. Theexception is for LIG made with O₂ in the chamber, which shows asignificantly lower 2D/G ratio of ˜0.55 as well as a much higher degreeof defects (higher D/G ratio). This could be due to the higher oxidationinduced by the O₂ environment, which can be related to the rough edgesand large pores observed in the SEM images. LIG made with H₂ in thechamber also shows a slightly increased D/G ratio, most likely becauseof the reducing environment, which prevents the decomposition orrearrangement of the defects within the graphitic structures. Yet nosignificant correlation could be found between the Raman spectra and thesuperhydrophobicity.

The low surface energy of C—F bonds can yield superhydrophobic surfaces.[Wang 2016; Lin 2011; Zha 2011; Singh 2013; Li 2014]. Here, theinventors of the present invention also tried to introduce C—F bondinginto the LIG structures using SF₆ gas in the chamber. SF₆ is anon-flammable gas commonly used as the dielectric medium in electronicsmanufacturing, yet it is able to decompose to form reactive F speciesunder extreme conditions. [Chu 1986; Tsai 2007]. Since SF₆ gas has ahigh absorbance at 10.6 μm, a 9.3 μm CO₂ laser is used to prepare LIGsamples when using SF₆ in the chamber, and FIGS. 13A-13F show thecharacterization of the samples. The typical LIG characteristics of aporous structure and D/G/2D peaks could be observed from the SEM imagesand the Raman spectrum (FIGS. 13A-13B). A significantly higher watercontact angle of 162° was achieved. A second video taken (available athttps://www.youtube.com/watch?v=qAuyVgYI9m8) that showed the waterdroplet bouncing on the surface of this LIG sample with SF₆ in thechamber until it settles on the neighboring PI film. High F-content(˜10%) of the LIG surface was confirmed by XPS as shown in FIGS.13C-13F. Both CF₂ (689 eV) and CF (687 eV) bonds are detected in the F1s spectrum and the tailing part for C 1s spectrum. [Zhao 2014; Romero2015].

Interestingly, elemental S was also identified by the peak position ofthe S 2p peak (164.5 eV). The SF₆ molecules decomposed under laserirradiation into elemental S that is deposited on LIG surface whileactive F species functionalized the graphene structures. To furtheranalyze the degree of F-functionalization throughout the entire LIGlayer (˜40 μm), an XPS depth profile was obtained for the LIG sample,and is shown in FIGS. 24A-24D. It is clearly observed that the Ffunctional groups are mainly distributed on the surface of LIG, possiblydue to the limited diffusion of the highly active F species into theporous structures of LIG. The abundance of CF₂ (689 eV) decreases muchfaster than the CF (687 eV) component, as shown in FIG. 24C. Differentlaser duty cycles were also applied to the LIG made with SF₆ in thechamber, and the acquired contact angles and F content are plotted inFIG. 25. Generally, higher laser duty cycles induce higher F contentsince more active F species are generated. A laser duty cycle of 4% ischosen as the optimal condition since it reaches a high contact angle(162°) but still maintains a relatively high C content of 86%.

To evaluate the stability of various superhydrophilic orsuperhydrophobic LIG surfaces obtained under different fabricationconditions, the inventors of the present invention re-tested the contactangles of the LIG samples after being under ambient conditions for oneweek and one year, and the results are shown in FIG. 27. As shown, thesuperhydrophilicity was maintained after one year, while thesuperhydrophobicity remained unchanged after one week, with slightdecreases in contact angles observed if kept in the air for extendedperiods of time.

Also, to evaluate the robustness of the superhydrophobic LIG, theinventors of the present invention performed different surfacetreatments for the LIG made with Ar in the chamber; thesuperhydrophobicity was maintained with: 1) blowing air at the surfacefor 1 min; 2) bending 100 times; 3) soaking in ethanol for 1 min; or 4)soaking in acetone for 1 min. However, the LIG tends to come off fromthe PI surface if sonicated in water for 1 min, and becomessuperhydrophilic if treated with O₂ plasma for 10 s. This post O₂ plasmamodification could make the patterning of two disparate surfaces(superhydrophobic next to superhydrophilic) via masking and exposure ahighly desirable quality of this technique. In general, thesuperhydrophobic LIG samples has shown good stability and robustness,while the superhydrophobicity was lost with intense treatments such assonication or surface oxidation, both of which are expected to affectthe morphology or graphene-like nature of the LIG materials.

Another important parameter to evaluate towards hydrophobicity is thehysteresis between the advancing contact angle and receding contactangle. [Gao 2006]. FIGS. 28A-28F show the advancing and receding contactangles for three kind of superhydrophobic samples demonstrated: LIG madewith Ar in the chamber shows the highest hysteresis of 12° in contrastto 4° and 5° for LIG made with H₂ and SF₆, respectively. This differenceresults from the lower O content for LIG made with H₂, and theF-functionalization for LIG made with SF₆.

While superhydrophobic structures and surfaces could have variedapplications [Zhang 2008], two examples, water/oil separation andanti-icing, are demonstrated in FIGS. 29A-29F and FIGS. 30A-30F. Forwater/oil separation (FIGS. 29A-29F), a LIG filter is produced by firstusing a high laser power (a laser duty cycle of 10% at a rastering speedof 3 cm/s) to create ˜100 μm holes in the PI sheets, and then using Arin the chamber to afford a superhydrophobic surface on the poroussubstrate. Interestingly, despite the existence of the ˜100 μm holes,the LIG filter still maintains a high contact angle of 155°, whichallows CHCl₃ to pass through the filter while water is repelled. Thevideo of the separation process was shown in a third video taken(available at https://www.youtube.com/watch?v=D1vexX-ZjVA).

For the anti-icing application (FIGS. 30A-30F), the comparison is madebetween superhydrophilic LIG made with air assist and superhydrophobicLIG made with Ar in the chamber. At −15 to −20° C., the water droplet(˜0° C.) sticks on the surface of LIG made in air even though tilted at45°, and ice consequentially forms. Conversely, LIG made with Ar in thechamber, being superhydrophobic, does not permit freezing to ensue. Iceforms only on the PI substrate, similar to the case of F-functionalizedGNRs. [Wang 2016].

FIGS. 14A-14D show the performance of LIG microsupercapacitorsfabricated with LIG made with air in the chamber compared to O₂ in thechamber. [Lin 2014; Peng I 2015; Peng II 2015]. LIG microsupercapacitorsmade with O₂ in the chamber has a significantly improved specificcapacitance (3×), energy density, and power density when compared withthe LIG sample made with air in chamber under the same laser duty cycleof 2%. This performance can be further improved by increasing the laserduty cycle to 5% with O₂ in the chamber where a specific capacitance of37 mF/cm² was achieved (FIGS. 31A-31B). The increased performance shouldpartially result from the enhanced hydrophilicity that provides bettercontact with the H₂SO₄/PVA electrolyte. [Li 2016].

Another important factor is the increased degree of defects and activesites when using O₂ in chamber, as observed in the Raman spectra inFIGS. 12A-12E. This is expected to improve the charge storageperformance of graphene materials, as is described theoretically andexperimentally. [Lin 2014]. In general, the enhancement insupercapacitor performance underscores the utility of the controlledatmosphere chamber for LIG preparation.

Accordingly, the inventors of the present invention have successfullydemonstrated the fabrication of LIG under various gas atmospheres with ahome-made controlled atmosphere chamber device. LIG samples withdifferent surface morphologies and surface chemistries have beenobtained, thus generating superhydrophilic or superhydrophobic LIGsurfaces depending on the gas environment introduced. The as-producedLIG structures can be directly used for improved microsupercapacitors,oil/water separation, and anti-icing films, all afforded by the variedsurface properties in the LIG. This laser fabrication method incontrolled gas atmospheres will allow for further broad-based LIGmaterials development.

The flow rates of the gas can depend on the capability of the flowcontroller. In some embodiments, an adjustable flow rate was usedbetween 0 and 1000 sccm. Any kind of gas mixtures can be used as soon asit is safe to do so, with examples including Ar/H₂, Ar/SF₆, H₂/SF₆,Ar/NH₃, H₂/NH₃, or even three- or more-component-mixtures. The ratio ofthe gas mixtures can be controlled by adjusting the flow rate of eachindividual gas. The pressure range can be between 0 to 2 bar due tosafety concerns (ZnSe window can only withstand a certain pressure withcertain thickness), yet higher pressure ranges can be achieved with athicker ZnSe window. The material of the window is not limited to ZnSe,other materials (quartz, etc.) can be used as long as it does not blockthe laser at certain wavelengths (10.6 μm, 9.3 μm, 1.06 μm, etc.). Thesize of atmosphere chamber can also be adjusted depending on theapplication of interest. For instance, an atmosphere chamber of ˜20 cmdiameter (with a 12×12 cm ZnSe window) has been utilized in embodimentsof the present invention. Precursors used in this atmosphere chamberinclude polyimide and other carbon precursors mentioned above, as wellas other types of materials (such as metal, for example).

Further Details for Fabrication of LIG Samples Under Different GasAtmospheres

Fabrication of LIG in Different Gas Atmospheres.

Laser induction was conducted on commercial PI (Kapton®, thickness 127μm, McMaster-Carr, catalog #2271K6) film with a XLS10MWH (UniversalLaser Systems) laser platform, equipped with a 10.6 μm CO₂ pulsed laser(75 W) and a 9.3 μm CO₂ pulsed laser (50 W). The same image density of1000 pulses/inch in both axes and a scan rate of 15 cm/s were used forall experiments. Typically, the laser duty cycle of 2% is used for thefabrication of LIG, but different laser duty cycles have been used forspecific experiments. Laser duty cycle is the percentage of time thatthe laser is turned on at the rated power for each laser spot; the laseris turned off for the rest of the time. 2% laser duty cycle is alsoreferred to as 2% laser power in the control software of the laserplatform, and it can be understood as the average laser power over theduration of each laser spot. For LIG made with gas assist (air or 3%H₂/Ar mixture), a nozzle provided with the instrument was used to blowthe selected gas towards the laser spot, while the general atmospherewithin the laser platform was still air at ambient pressure, as shown inFIG. 10A. For LIG made with the controlled atmosphere chamber (O₂, air,Ar, H₂, or SF₆), a controlled atmosphere chamber was used to allowdifferent gases to flow through the chamber at 1 atm while synthesizingthe LIG. A ZnSe window (thickness 6 mm) is mounted on top of the chamberto allow the CO₂ laser to irradiate the PI film, as shown in FIG. 10B.The flow rates used were ˜140 sccm for O₂, ˜140 sccm for air, ˜125 sccmfor Ar, ˜175 sccm for H₂, and ˜70 sccm for SF₆, all at ambient pressure.Note that Ar can be replaced by N₂ as the inert gas, and FIG. 32 showsthe superhydrophic LIG surface prepared with N₂ in the chamber. The LIGmade with SF₆ in the chamber sample was prepared with the 9.3 μm CO₂laser; all other samples were made with the 10.6 μm CO₂ laser.

Characterization.

SEM images were taken with a FEI Quanta 400 ESEM. TEM characterizationswere performed using a 200-kV JEOL 2100 Field Emission Gun TEM. Ramanspectra were recorded with a Renishaw Raman RE01 scope with 514 nmlaser. XPS was performed on a PHI Quantera SXM scanning X-ray microprobewith 200 μm beam size and 45° takeoff angle, and calibrated using C 1sat 284.5 eV.

Fabrication and Electrochemical Characterizations of LIGMicrosupercapacitors.

LIG was patterned into interdigitated electrodes with a length of 4.1mm, a width of 1 mm, and a spacing of ˜300 μm between two neighboringmicroelectrodes. Colloidal silver paint was applied on the common areasof both electrodes for better electrical contact, and the electrodeswere extended with conductive copper tape. A Kapton® PI tape wasemployed followed by an epoxy sealing to protect the common areas of theelectrodes from electrolyte (H₂SO₄/PVA polymeric gel), which was laterapplied on to the active area of the microsupercapacitor devices anddried in a vacuum desiccator. The electrochemical performances of themicrosupercapacitors were characterized by CV and galvanostaticcharge-discharge experiments using an electrochemical station, and thespecific capacitance, energy density, and power density were calculatedas previously reported. [Lin 2014; Peng I 2015; Peng I 2015; Li 2015].

Utility and Variations

The present invention provides a process to tune the properties of LIGby changing the gas atmosphere of the LIG fabrication process. Thesuperhydrophobic LIG obtained from this invention can be used for waterrepelling applications such as oil/water separation, anti-icing films,or other related areas. The LIG prepared with O₂ in chamber can be usedas improved electrodes for high-performance supercapacitors or otherrelated applications. Other areas of application are also possibledepending on the gas atmosphere and properties of LIG.

Variations in this invention may include but are not limited to:different kinds of gases used in the fabrication process including mixedgases, differing pressures, use of a vacuum (reduced pressures from 1atm to 10⁻⁸ Torr), higher pressures (>1 atm up to 375 atm), differentgas pressure and flow rate, different substrates, different laserconditions, or any variations of the invention deemed logical extensionsof the invention.

Further information regarding the present invention is set forth in theinventors paper Y. Li et al., “Laser-Induced Graphene in ControlledAtmospheres. From Superhydrophilic to Superhydrophobic Surfaces,” Adv.Mat. 2017, 29(27), 1700496 and supporting information, which are herebyincorporated by reference in their entirety for all purposes.

Laser-Induced Graphene from Polysulfones

Graphene is formed on the surface of laser-irradiated aromaticpolysulfones (the class of polymers having aryl-S(═O)₂-aryl in therepeat unit). In particular, experimental results reported belowindicate that the following three polymers produce LIG:

referred herein as “polysulfone” or “PSU;”

referred herein as “polyethersulfone” or “PES;” and

referred herein as “polyphenylsulfone” or “PPSU.”

Hereinafter the term “aromatic polysulfone” refers to any polymer withthe aryl-S(═O)₂-aryl subunit, whereas the term “polysulfone” indicatesspecifically the polymer depicted above.

One aspect of the invention therefore relates to a process includingirradiating aromatic polysulfone (e.g., polysulfone, polyethersulfone,or polyphenylsulfone, abbreviated PSU, PES, and PPSU respectively) withlaser to form graphene on the surface of the polymer, and optionallyseparating the so-formed graphene from the polymer.

The PSU-LIG and PES-LIG and PPSU-LIG prepared by the foregoing processform another aspect of the invention. That is, the invention provides anaromatic polysulfone having graphene on its surface. More specifically,the LIG is sulfur-doped graphene. In the aromatic polysulfone startingmaterial, sulfur is present solely in the form of —C—S(═O)₂—C-functionalgroups. The laser-induced graphene fabrication method of the inventioncauses the incorporation of sulfur into the graphene, that is, theformation of —C—S—C— and/or C—S—H bonds. Therefore, a specific materialafforded by the fabrication method of the invention is an aromaticpolysulfone having sulfur-doped graphene on its surface.

Polysulfone, polyethersulfone, and polyphenylsulfone are highly used innumerous applications including medical, energy and water treatment andthey are critical components of polymer membranes. It has been shownthat LIG fabrication on PSU, PES, and PPSU results in conformalsulfur-doped porous graphene embedded in polymer dense films or poroussubstrates using reagent- and solvent-free methods in a single step. Ithas further been demonstrated that such materials are applicable asflexible electrodes with enhanced electro-catalytic hydrogen peroxidegeneration, as antifouling surfaces and as antimicrobial hybridmembrane-LIG porous filters. The properties and surface morphology ofthe conductive PSU-, PES-, and PPSU-LIG can be modulated using variablelaser duty cycles. The LIG electrodes showed enhanced hydrogen peroxidegeneration compared to LIG made on polyimide, and showed exceptionalbiofilm resistance and potent antimicrobial killing effects when treatedwith Pseudomonas aeruginosa and mixed bacterial culture. The hybridPES-LIG membrane-electrode ensured complete elimination of bacterialviability in the permeate (6 log reduction), in a flow-throughfiltration mode at a water flux of ˜500 L m⁻² h⁻¹ (2.5 V) and at ˜22000L m⁻² h⁻¹ (20 V). Due to the widespread use of PSU, PES, and PPSU inmodern society, these functional PSU-, PES-, and PPSU-LIG surfaces havegreat potential to be incorporated into biomedical, electronic, energyand environmental devices and technologies.

It has further been shown that LIG can be fabricated from PSU, PES andPPSU under ambient conditions, producing LIG layers doped with sulfurdue to the inherent sulfur content in the polymers. The applicabilitywas demonstrated as electrodes on dense polymer films as well as onprefabricated porous polymer membranes. It has also been shown that LIGderived from these polymers and that their incorporation into devicesenhanced electrical, antibacterial and anti-biofilm activity. Moreover,since these materials are the backbone of the membrane filtrationtechnology, we demonstrate a flow-through membrane device with activemicrobial killing. This is of significant importance for membranetechnology due to the persistent fouling challenges inherent to membraneprocesses. Since sulfur doped graphene has already proven to be asuperior electro-catalyst for oxygen reduction reactions used in fuelcells and batteries, this invention might facilitate added functionalityin such devices, especially imparting biofilm resistance. Theseelectrodes and membranes might also be effectively used for cathodes inmicrobial fuel cells, to address the challenge of biofilm formation andlower performance. Moreover, due to its high electrical and thermalconductivity and the versatility of the polymer substrate materials,incorporation of LIG into energy, medical, and environmentalapplications is now possible.

LIG Fabricated on PSU, PES, and PPSU Polymers

FIG. 34A illustrates PSU, PES and PPSU polymers (PSU-class polymers)sheets irradiated using a CO₂ laser (10.6 μm) in ambient atmosphere toproduce conformal LIG fixed in the underlying polymer matrix. PSU-LIG,PES-LIG and PPSU-LIG laser induction was conducted on PSU, PES, and PPSUsheets (˜100 μm thickness) made from commercial polymer pellets obtainedfrom BASF (Ultrason, PSU (S 6010, 60 kD); PES (E 6020P, 75 kD); PPSU (P3010, 48 kD)). For thin films of PSU and PES, the polymer pellets (2.5g) were dissolved in dichloromethane (20 mL) and the solution was pouredinto a glass Petri dish (inner diameter 11.5 cm). To slow theevaporation of the dichloromethane, an inverted funnel was placed on topof the petri dish. For PPSU, the polymer pellets (2.5 g) were dissolvedin DMF (20 mL) and the solution was poured into the glass Petri dish(inner diameter 11.5 cm). The solvent was evaporated under vacuum at 60°C. When the solvents were evaporated, the films were removed andmeasured to have an average thickness of 94.6±5.5 mm for PES, 102.5±4.2μm for PSU, and 106.6±7.4 μm for PPSU. For the generation of LIG on thesurfaces, a VLS 3.50 (Universal Laser Systems) laser platform, equippedwith a 10.6 μm CO₂ pulse laser (50 W, 2.0 inch Lens Kit) was used. Animage density of 70 PPI (pulses per inch) and a scan rate of 25% wereused for all experiments with variable laser duty cycle (5.0 to 9.0%).For PES-LIG and PPSU-LIG the laser was focused, while for PSU-LIG, thelaser was defocused by 0.4 cm, meaning that the PSU film was moved 0.4cm closer to the cutting lens from a focused position. PSU-LIG, PES-LIGand PPSU-LIG were made in ambient conditions in the presence of air. Thegeneral atmosphere within the laser platform was still air (1 atm). Anozzle provided with the instrument was used to blow air towards thelaser spot.

The importance of the synthesis of LIG on PSU-class polymers in ambientatmosphere lies in the widespread use of PSU-class polymers inbiomedical, energy and water treatment technology, generating embeddedgraphene coatings inherently doped with sulfur. The conductive,inherently black LIG on the PSU-class polymers can be simply patternedin any shape on the flexible polymer films. See FIG. 34B. The laser spotfocus was utilized to generate LIG on PSU films. In this case, LIG wasformed when the substrate was brought closer to the cutting lens givinga defocused spot. In contrast, PES-LIG and PPSU-LIG were made with afocused laser spot on the substrate surface.

As shown in FIG. 34C, the X-ray diffraction (XRD) pattern of PSU-, PES-and PPSU-LIG showed peaks at 25.9° (2θ) for the 002 plane and a secondpeak at 42.9° (2θ), which corresponded to the 100 plane. The peak at25.9° (2θ) gave an interlayer spacing (Ic) of 3.4 Å and indicated a highlevel of graphitization, and the peak at 42.9° (2θ) was associated withan in-plane structure. The peak at 25.9° (002) shows asymmetry and withtailing at smaller 20 angles also points to an increased Ic. It wascalculated that the crystalline sizes along the c axis (Lc) and domainsize along the a axis (La) for all three LIG types using equations (1)and (2) and are shown in TABLE 2 (crystalline sizes of PSU class LIGsalong c axis (Lc) and domain size in the a axis (La)). The highest Lcwas found for PSU-LIG (6.4 nm), whereas La was highest for PPSU-LIG (7.8nm).

$\begin{matrix}{{Lc} = \frac{0.89\lambda}{{B_{1/2}\left( {2\theta} \right)}{Cos}\; \theta}} & (1) \\{{La} = \frac{1.84\; \lambda}{{B_{1/2}\left( {2\; \theta} \right)}{Cos}\; \theta}} & (2)\end{matrix}$

TABLE 2 Materials Lc (nm) La (nm) PSU 6.4 7.6 PES 4.2 7.2 PPSU 4.2 7.8

As shown in FIG. 34D, the Raman spectra of PSU-class LIG showscharacteristic peaks for graphene at ˜1,350 cm⁻¹ (D peak), ˜1,580 cm⁻¹(G peak) and ˜2,700 cm⁻¹ (2D peak). The D peak induced by defects in sp²carbon bonds, the G peak is the first order allowed peak, whereas the 2Dpeak originates from second order zone-boundary phonons. The 2D peaks ofPSU-, PES- and PPSU-LIG were fitted to only one Lorentzian peak centeredat 2,700 cm⁻¹, similar to single layer graphene. Larger full widths athalf maxima for PSU-LIG (˜117 cm⁻¹), PES-LIG (˜87 cm⁻¹) and PPSU-LIG(˜94 cm⁻¹) were observed. A high degree of graphene formation issupported by the D/G intensity ratio for the PSU-class LIGs, and the2D/G intensity ratio observed between 0.5-0.6 indicated goodgraphitization in the PSU-class of LIG. As shown in FIG. 34E, X-rayphotoelectron spectroscopy (XPS) gives the material surface chemicalcomposition information of the elements with electronic state and showedC1s, O1s and S2p peaks for the LIG at ˜285.5 eV, ˜534 eV and ˜167 eV,respectively. This confirmed the sulfur content in the graphene. Theratio of the intensity of the C s and O1s peaks (C/O of 13.21, 9.75 and9.03) for PSU-, PES- and PPSU-LIG, respectively, indicated that PSU-LIGhad significantly lower oxygen content compared to PES- and PPSU-LIG.

The SEM images at different resolutions show the highly porous foam-likestructure for the PSU-class LIG. The morphology of the LIG is highlydependent on the fabrication conditions, but morphology of PSU-LIG(FIGS. 35A-35C) was notably different compared to PES-LIG (FIGS.35E-35G) and PPSU-LIG (FIGS. 35I-35K). It was observed that the obtainedPSU-LIG was less porous as compared to the PES- and PPSU-LIG.Cross-sectional SEM images supported this observation where PES- andPPSU-LIG show a highly porous structure compared to PSU-LIG (FIGS. 35C,35G, and 35K). Fiber-type structures were seen with increased laser dutycycles for PES- and PPSU-LIG. Similarly, with a higher laser duty cycle,porosity of all LIG increases. Similar to LIG made from polyimide, TEMimages for the PSU-class LIG shows wrinkles of graphene layers on thesurfaces (FIGS. 35D, 35H, and 35L, and high resolution images of TEMshow the graphene fringes and the characteristic d-spacing (0.34 nm).

The sulfur content in the graphene material was confirmed usinghigh-resolution XPS spectra and de-convolution of C1s and S2p showed thebonding type present on the surface See FIGS. 36A-36I. For each LIGtype, the Cis gave C═C and C—O at 284.8 eV and 285.8 eV respectively(FIGS. 36A-36C). The S2p spectra showed two kinds of bonding at ˜164 eVand ˜168 eV, which corresponds to C—S and C—SO_(x), respectively (FIGS.36D-36F). Whereas, S2p spectra for the polymer substrate only showedC—SO_(x) bonding at ˜168 eV (FIGS. 36G-36I). The insertion of sulfur inthe graphene skeleton can be explained as C—S—S and —C═S bonding at163.9 eV and 165.3 eV, respectively. The overall sulfur content measuredfor PSU-, PES-, and PPSU-LIG were 3.3, 1.6 and 2.6%, respectively.

Hydrogen Peroxide Generation

Hydrogen peroxide (H₂O₂) has wide interest in the energy andenvironmental technology in fuel cells, as a propellant in rocketry, andas a strong oxidizer and disinfectant. H₂O₂ generation was shown usingPSU-class LIG at different voltages in 0.05 M NaCl and 0.05 M Na₂SO₄ aselectrolytes See FIGS. 37A-37F. The highest amount of H₂O₂ was observedusing electrodes made from PSU-LIG at 2.0 V (FIG. 37A) using aqueousNaCl as the electrolyte. This material contained the highest amount ofsulfur compared to the LIG derived from PES and PPSU, which might beattributed to the differences in preparation method. The H₂O₂ generationin Na₂SO_(4(aq)) was directly proportional to the voltage (FIGS.37C-37E), whereas in NaCl_((aq)), we observed that the highest H₂O₂generation was at 2.0 V with PSU- and PPSU-LIG and at 2.5 V for PES-LIG.In this case, active chlorine generation at higher voltages can rapidlyreact with H₂O₂ resulting in optimal conditions at a lower appliedvoltages. The enhanced H₂O₂ production as compared to LIG made frompolyimide indicates that the sulfur-doped PSU-class LIG might beadvantageous in many energy and environmental applications. Compared tographite electrodes, H₂O₂ was not measured in either tested electrolytein 3 h of measurement. The CV curves for the PSU-class LIG electrodeswere recorded in 0.1 M Na₂SO₄ and were typical of a non-metal doped LIGsample.

LIG Inhibits Biofilm Growth

There is exceptional resistance of LIG made from polyimide to biofilmformation. The susceptibility for biofilm formation was investigated oneach LIG type (see FIG. 38) and observed extremely bio-film resistantsurfaces, similar to polyimide LIG. Experiments were compared tographite and PSU-class polymer substrates upon which thick biofilmincluding live and dead bacteria and extracellular polymeric substances(EPS) were observed. Three-dimensional (3D) visualization of the biofilmwas imaged with IMARIS-Bitplane software, and represents the averagedquantitative values of biofilm observed. More specifically in FIG. 38,mostly EPS and live biomass were found on the control graphite surface,whereas on the polymer substrates mostly dead and live biomass wasobserved. The highest biomass ˜31 μm³/m² was observed with the graphitecontrol. LIG surfaces showed exceptionally low amounts of biomass. Sincethe PSU-class of polymers is one of the most popular synthetic polymermaterials used for the fabrication of membranes and used for multiplemembrane applications including gas and aqueous separation processes,porous LIG on PSU membranes can tailor the surface properties includingfouling-resistance, superhydrophilicity or superhydrophobicity andelectrical conductivity.

Important factors for aqueous applications of PSU-class membranes thatgovern biofilm formation on the surfaces include water wettability andsurface charge. The water wettability of the LIG as measured by watercontact angle analysis was significantly more hydrophilic (PSU-LIG44.0°±1.8; PES-LIG 47.5°±1.5 and PPSU-LIG 39.0°±2.1) compared to thepolymer substrate (PSU 74.5°±1.9, PES 69.3°±1.2, and PPSU 68.1°±2.9), orgraphite (61.3°±6.6). The zeta potentials were determined and we foundthat all the surfaces were negatively charged. The zeta potential at ˜pH7.4 was between −65 mV to −102 mV for all polymer substrate and LIGsurfaces, which were less than the graphite surface (−117 mV). Takentogether, the mechanism for low biofilm formation on LIG surfaces wasmost likely similar to LIG made on polyimide, which was explained as acombination of physical, chemical and biological properties of the LIGsurfaces. However, the presently described LIG has similar complextextures to PI-LIG including extremely rough surfaces of variableporosity at the micron-size level, including foam- and fiber-liketextures, yet with differing chemical compositions, which might indicatethat texture is also an important factor in the mechanism of action.Highly hydrophilic surfaces can absorb less organic matter reducingbiofouling. Moreover, the negative surface charge of many bacteria e.g.P. aeruginosa (−23.3 mV) might lead to electrostatic repulsion withnegatively charged surfaces, although the vulnerability of highlynegatively charged surfaces to organic fouling might lead to adverseoutcomes.

Antibacterial Action of PSU Class Electrodes

The PSU-class LIG samples were configured as electrodes and were used todecontaminate P. aeruginosa (˜1×10⁶ CFU/mL) contaminated solutions atvoltages ranging from 1.5 to 2.5 V (FIGS. 39A-39F). The PES-LIGelectrodes eliminated bacterial viability in the solution the fastest,where a 6 log bacterial removal was seen within 2 hours at 2.5 V,followed by PPSU-LIG and PSU-LIG. The killing efficiency was directlyrelated to the applied voltage, and the lowest voltage tested (1.5 V)gave 66-97% bacteria killing in 6 h operation. The mechanism of bacteriainactivation is mostly likely a combined electrical and chemicaleffects. In the present case, the electrical effects might dominatesince we observed highest H₂O₂ generation with PSU-LIG at 2.0 V, butmore effective bacterial killing was observed at 2.5 V. Compared topolyimide LIG which gave only a 3.5 bacterial log reduction after 9 hoperation at 2.5 V, the sulfur-doped PSU-class LIG was more effective,since in all cases more than 6 bacterial log reduction was observedwithin 4 h. Similarly, at 2.0 V with polyimide LIG only ˜1 log reductionwas observed, compared to a 6 log reduction within 4 h for PSU-classLIG. Similar highly effective bacterial deactivation was seen using amixed bacterial culture obtained from real secondary treated wastewaterinvestigated at 2.5 V. Such enhancements in activity highlights that LIGcan be further tailored by using PSU-class polymer sources that providevariability in the heteroatomic composition of the graphene, and mightlead to enhanced properties.

LIG On PES Membranes

LIG was directly fabricated on different commercial and self-made PESmembranes, which were characterized using Raman, SEM and XPS. FIG. 40Aillustrates LIG fabricated on the porous membrane substrate (PES UP150),including a photograph of the circular membrane coupon. The LIG on theporous substrate shows a similar large porous structure compared to LIGmade on dense films (FIG. 40B), and the D, G and 2D Raman peaks at˜1,350 cm⁻¹, ˜1,580 cm⁻¹ and ˜2,700 cm⁻¹, respectively (FIG. 40C),confirmed the graphitization of the surface of the UP150 membrane. XPSof UP150-LIG confirmed the sulfur content (C—S bonding) in the grapheneskeleton, which was not present in the UP150 membrane substrate. Themixed bacterial culture was passed through the LIG as fabricated on aseries of commercial and self-made PES membranes (FIG. 40D) and it wasfound that the highest bacterial removal rate (˜96%) was with LIG on theself-made membrane PES-1.

The LIG made on the porous PES membranes were extremely resistanttowards biofilm formation using the mixed bacterial culture asdemonstrated with the UP150-LIG filter (FIG. 40E). Similar to the densefilm substrates, the porous control UP150 PES membrane showed largeamounts of biomass compared to the UP150-LIG, which showed nearly abiofilm-free surface. To demonstrate a porous electrode LIG-filter,carbon threads were attached to the LIG-membranes and placed onemembrane on top of another for a stacked membrane flow-through systemdesign (FIG. 40F). In this configuration all LIG-membranes showed 6bacteria log reductions in the permeate at 2.5 V at flow rates of ˜500 Lm⁻² h⁻¹ with mixed bacterial culture (FIG. 40G). The UP150-LIG filterswere also tested at ultrahigh flow rates (˜22000 L m⁻² h⁻¹) andbacterial removal depended on the applied voltage. Complete bacterialinhibition (6 bacterial log reductions) could be achieved when thevoltage was set at 20 V (FIG. 7g ). Using samples of characterized realsecondary treated wastewater 90-99.9% inhibition of bacteria wasachieved at 10-20 V at a rate of ˜500 L m⁻² h⁻¹.

Fabrication of PSU and PES Laser-Induced Graphene (LIG)

For PSU-LIG and PES-LIG, laser induction was conducted on PSU and PESsheets (˜100 μm thickness) made from commercial polymer pellets(Ultrason, BASF, PSU (6010, 60 kD), and PES (6020P, 75 kD)). To make thethin sheets, the polymer pellets (2.5 g) were dissolved indichloromethane (20 ml). The solution was poured into a glass Petri dish(inner diameter 11.5 cm). To control the evaporation of thedichloromethane, a funnel was placed on top of the Petri dish upsidedown. When the solvent was completely evaporated, the film was removedand measured to have an average thickness of 85±17 micrometers for PES,and 92±16 micrometers for PSU.

AVLS 3.50 (Universal Laser Systems) laser platform, equipped with a 10.6μm CO₂ pulse laser (50 W) was used. The same image density of 70 PPI(pulses per inch) and scan rate of 25% were used for all experimentswith variable laser power (5.0 to 9.0%). PSU-LIG and PES-LIG made inambient environment in presence of air, the general atmosphere withinthe laser platform was still air (1 atm).

The PSU and PES LIG samples were characterized using SEM images, Raman,contact angle, and XPS. The SEM images showed different morphologiesusing different laser powers. For example, PSU made using 5% or 6% laserpower (50 W) gave smoother surfaces in comparison to PSU-LIG made with7-9% laser power. PSU-LIG made with 7% laser power was observed to havean intermediate roughness with larger surface pores. 8%, and 9% PSU-LIGwere the roughest, and unique round spherical structures were present atthe surface.

For PES-LIG however, the morphology was yet very different than thatobtained for PSU-LIG. PES-LIG gave in general a finer roughness. Withinthe PES-LIG samples made at different powers (5%-9%), differentmorphology was observed. For example, PES-LIG made with 5% contained asurface of many ridges and large pores, whereas a finer roughness wasobserved for PES-LIG 6%-9%. PES-LIG 6%-8% gave similar morphology, andPES-LIG 9% gave slightly rougher coral-like structures. PES-LIG wereobserved by SEM images to all be very highly porous. Differences weremore easily seen in high resolution SEM. Especially PSU-LIG 5% wasdifferent and gave larger globular-like structure than PSU 6%-9%, whichwere more highly porous. High resolution SEM for PES-LIG all showed veryhighly porous structures. Cross-sectional images also show difference inPSU-LIG 8%, and PES-LIG 8%, and show that PES-LIG 8% was more porous,and gave a thicker layer (ca. 150-200 micrometers) than PSU-LIG 8% (ca.100 micrometers).

For both samples PSU-LIG 8% and PES-LIG 8%, a strong fluorescence wasobserved when excited by the laser (433, and 620 nm) present in the CLSMmicroscope.

Characterization of the presence of graphene was performed with Ramanspectroscopy. Three major peaks were observed that are characteristic ofgraphene: the D peak at ˜1350 cm⁻¹ induced by defects or bent sp²-carbonbonds, the first order allowed G peak at ˜1580 cm⁻¹, and the 2D peak at˜2700 cm⁻¹.

The contact angle measurement showed that the hydrophilicity of thePSU-LIG and PES-LIG was similar, more hydrophilic than the substratesPSU or PES, or a graphite sheet as controls.

XPS further characterized the atomic composition of the surfaces. C, O,S and N were recorded, and certain trends were observed. For example,for PES-LIG made with lower laser powers gave less sulfur incorporationto the LIG. For example, only 2.7% S was observed for 5% PES-LIGcompared with 6.1% S observed in 8% PES-LIG. However, less S (3.2%) wasseen at the highest laser power used (9%). The S2p peak incorporated 2distinct signals appearing at ˜169 eV and ˜164 eV. This indicated morethan one form of sulfur in the surface layer. The PES-LIG (8%) had alarger signal ratio (˜164 eV/˜169 eV), than the PES-LIG made at lowerlaser powers. For 9% PES-LIG however, there was mainly the signal at˜164 eV. For PSU-LIG, there was no clear trend in the sulfurcomposition, however, PSU-LIG 6% gave the highest amount of incorporatedsulfur at 4.6%. Also, similarly to PES-LIG, PSU-LIG gave a new sulfursignal at 164 eV.

PES-LIG with Improved Quality—Defocusing

PES sheets were prepared as described above. XLS10MWH (Universal LaserSystems) laser platform, equipped with a 10.6 μm CO₂ pulse laser (75 W)was used. The same image density of 1000 PPI (pulses per inch) and scanrate of 10% (15 cm/s) were used for all experiments with laser power(10%). The sample was maintained in ambient environment in presence ofair, the general atmosphere within the laser platform was still air (1atm).

Samples were placed above the focal plane. Focal distance of the lens inthe apparatus was 2.0″ inches, and samples were offset from the focalplane by up to about 1.27 mm (about 50 mils). (It should be noted thatthe samples could also be offset below the focal plane).

Sheet square resistance was measured using a Keithely 195A four-pointprobe.

A sharp decrease in square resistance was found with defocusing of up to30 mils (1.5% of the laser focal length), further increasing beyondabout 40 mils (greater than 2% of laser the focal length). The laserfocal length will vary depending upon the optics used for the laser.Increasing the defocusing will increase the effective beam size andresult in more overlapping lases.

The Raman spectra of these materials were consistent with the sheetresistance. The material obtained with the 30 mil defocus showing thebest D/G ratios as well as the most intense 2D peak, correlating withthe quality of the LIG.

PES-LIG with Improved Quality—Multiple Exposures

PES sheets were prepared as described above. XLS10MWH (Universal LaserSystems) laser platform, equipped with a 10.6 μm CO₂ pulse laser (75 W)was used. The same image density of 1000 PPI (pulses per inch) and scanrate of 10% (15 cm/s) were used for all experiments with laser power(10%). The sample was maintained about 30 mils above the laser lensfocal plane (i.e., about 1.5% of the focal length), in ambientenvironment in presence of air, the general atmosphere within the laserplatform was still air (1 atm).

Rastering was repeated several times, exposing the same portions of PESfilm to multiple pulses. Sheet square resistance was measured as above.

A further decrease in sheet square resistance was observed in sampleswith double and triple exposure. A thrice-lased sheet showedextraordinary 1.5 Ohm/sq resistance, indicating a highly conductivesurface. Further exposures provided no improvement and increased theresistance.

Raman spectra have also confirmed that the LIG with the best observedsheet resistance showed the highest-quality Raman spectrum in terms ofthe peak ratios evidencing higher quality graphene.

PSU-LIG with Improved Quality—Defocusing

PSU sheets were prepared as described above. XLS10MWH (Universal LaserSystems) laser platform, equipped with a 10.6 μm CO₂ pulse laser (75 W)was used. The same image density of 1000 PPI (pulses per inch) and scanrate of 10% (15 cm/s) were used for all experiments with laser power(8%). The sample was maintained in ambient environment in presence ofair, the general atmosphere within the laser platform was still air (1atm).

Samples were placed above the focal plane. Focal distance of the lens inthe apparatus was 2.0 inches, and samples were offset from the focalplane by up to about 1.27 mm (about 50 mils).

Sheet square resistance was measured as above.

A highly sharp decrease in square resistance was found with defocusingof up to 30 mils (1.5% of laser focal length) (from about 2300 Ohm/sq toabout 5 Ohm/sq), further increasing with defocusing rising beyond about40 mils (greater than 2% of laser the focal length).

Biofilm Growth Assay of PSU-LIG and PES-LIG (Laser-Induced GrapheneFabricated on PSU and PES)

The antibiofouling and antibiofilm properties of PSU-LIG and PES-LIGwere observed in a flow cell test. The setup for this test includednutrient media, a pump, and a flow cell chamber, which contained thesamples attached to a glass slide.

The control polymer (PSU or PES) and LIG samples were attached to glassslide with double sided tape and were placed inside the flow cell. Ingeneral, the samples were inoculated by flowing 50 ml bacteria culturethrough the flow cell at 2.5 ml/min, followed by up to 48 hours ofnutrient media. Different experiments were conducted with Pseudomonasaeruginosa PO1.

Pseudomonas aeruginosa PO1 was cultured. A 50 ml culture of thesebacteria in LB broth with an OD_(600 nm) of 0.1 was flowed into thechamber at 2.0 ml/min and out. This was followed by continuous flux of2.0 ml/min of LB media containing carbenicillin 150 mg/L for 48 hours.Carbenicillin was used to inhibit the growth of any interferingbacterial species.

Staining of the bacteria was performed with a live/dead kit (Invitrogen)by adding 1.5 μl Propidium iodide—to stain dead bacterial cells, 1.5 μlSyto 9—to stain live bacterial cells, and 100 μl fluorescentConcanavalin A, a carbohydrate binding protein (lectin) that adheres toEPS (Extracellular polymeric substances) secreted by bacteria, to 897 μlof 0.1 M NaCl. The samples were stained by adding 2-3 drops of thestaining mixture onto the surface, and afterward they were washed with0.1 M NaCl, and covered under aluminum foil (to prevent any interactionwith light from the environment) and imaged using CLSM (Confocal LaserScanning Microscopy). The biofilm was imaged using Z scanning. Multipleareas of the sample were observed, and the results were averaged. Theaverage biomass and biofilm thickness was quantified using MATLAB, witha pre-written program for biofilm image quantification called COMSTAT.IMARIS software was used to visualize and process the CLSM images toreconstruct a 3-D image from multiple microscopy images from a z-scan.Live bacteria, dead bacteria and EPS are colored green, red, and grey inthe images.

P. aeruginosa Biomass & Biofilm Thickness on PSU, PES, Graphite Sheet,PSU-LIG, and PES-LIG:

The testing was conducted with 5 samples—control polysulfone (PSU),control polyethersulfone (PES), control graphite paper, PSU-LIG(polysulfone-laser-induced graphene), and PES-LIG(polyethersulfone-laser-induced graphene). It was observed that thecontrols, which do not have LIG, have high density of dead cells, EPS,and live bacterial cells. Whereas, PSU-LIG and PES-LIG were almost voidof live and dead cells, and EPS.

CLSM images show that PSU and PES polymers have more bacterial contentswhen compared with PSU-LIG and PES-LIG samples.

H₂O₂ Generation by PSU-LIG and PES-LIG Electrodes Using 50 W Laser, 8%Laser Power in Air, Using a DC Voltage of 1.5, 2.0 and 2.5 V

PSU and PES-Laser-induced graphene for H₂O₂ Generation: Polysulfone andpolyethersulfone (thickness: ±100 μm) polymer sheets were prepared formpolymer pellets (Ultrason, BASF, PSU (6010, 60 kD), and PES (6020P, 75kD)) as described above. Laser scribing on polymer sheets was conductedwith a VLS3.50 (Universal Laser Systems) laser platform, equipped with a10.6 μm CO₂ pulse laser (50 W). The same image density of 70 PPI (pulsesper inch) and scan rate of 25% were used for electrodes with 8.0% laserpower. PSU-LIG and PES-LIG made in ambient environment in presence ofair, the general atmosphere within the laser platform was still air (1atm). Wires were glued onto the surfaces using commercially availableconductive carbon based glue.

PSU and PES-LIG Electrodes:

PSU and PES sheets were used for the PSU-LIG and PES-LIG fabricatedelectrodes. PSU-LIG and PES-LIG was directly written using the computercontrolled CO₂ laser applied on these PSU and PES films. Theseconducting PSU-LIG and PES-LIG coatings were used as the electrodes. Forthe tests, wires were attached to the electrodes by conductive glue.These electrodes were extended with electrical wires and then connectedto an electrochemical workstation.

Current and voltage characteristics for the LIG electrodes werecharacterized by using a testing setup. In this setup, a direct current(DC) power supply with variable voltage was used. The LIG containingsurface was partly immersed in 100 ml of 0.05 M NaCl solution in abeaker keeping the wires and conductive glue exposed to the air. Thevoltage was turned on and varied from 0-2.5 V, and the current andvoltage were measured by using multi-meters. Either PSU-LIG or PES-LIGelectrodes were used for the cathode and anode.

Generation of Hydrogen Peroxide by LIG Spacers:

Evaluation of hydrogen peroxide generation by LIG was done in the samesetup described in the methods above. Hydrogen peroxide concentrationwas measured by the DMP colorimetric method. DMP method is aspectrophotometric method using copper(II) ion and2,9-dimethyl-1,10-phenanthroline (DMP). A complex Cu(DMP)₂ ⁺ formed(bright yellow complex) with maximal absorbance at 454 nm and is stableunder ordinary light. The blank solution without H₂O₂ has a differentcolor, and differences of the absorbance between the sample and blanksolutions are approximately proportional to H₂O₂ concentration. The DMPwas purchased from Sigma-Aldrich (Israel). For an experiment, freshaqueous NaCl solution (0.05M) was added to the beaker. 1.5 V was appliedwith LIG coated surfaces fabricated with PSU-LIG and PES-LIG. The H₂O₂generation was measured from 1.0 ml samples taken from the solution. Inboth cases, the concentration increased with time. Maximum H₂O₂concentration with “PSU-LIG” was 2.57 mg/L after 3 hours of theexperiment at 2.0 V, whereas with “PES-LIG,” 1.99 mg/L H₂O₂ was measuredafter 3 hours of operation at 2.0 V.

Antibacterial Effect of PSU-LIG and PES-LIG Electrodes:

The antibacterial effect of the electrodes was measured by addition of abacterial culture of P. aeruginosa at ultra-high bacterial load (˜10⁷CFU/ml) or at high bacterial load (˜10⁶ CFU/ml) in the setup describedabove. The bacteria were grown in liquid media LB as described above.The culture was grown overnight with shaking at 30° C., and the bacteriawas pelleted by centrifugation at 4,000 rpm and washed with sterile PBS(2×) and then the bacteria was suspended in sterile PBS. The bacteriawere added to an aqueous solution of NaCl (0.05 M, 100 ml) containingthe LIG electrode at ultra-high bacterial load (˜10⁷ CFU/ml) or at highbacterial load (˜10⁶ CFU/ml). An electrical potential (1.5, 2.0, and2.5V) was applied and the CFU were monitored over time using spreadplate method. Colonies were counted after 24 hours of incubation at 30°C.

High Bacterial Loading and Ultra High Bacterial Loading Tests:

The change in the microbial population and percentage killing wasmeasured. A seven log bacterial reduction was seen with the ultra-highbacterial loading experiment after 6-hour operation at 2.5V and 2.0 V,whereas ˜2 log reduction was seen at 1.5 V with both PSU-LIG andPES-LIG. In general it was observed that the PES electrodes have higherkilling rate as compared to PSU-LIG. H₂O₂ bulk concentration was alsomonitored during the testing. In all cases, the testing run at 2.0 Vshowed the highest amount of H₂O₂ generated.

For high loading bacterial analysis, after 6 hours of operation, 6 logreduction of microbial populations were seen by PSU-LIG, and PES-LIGelectrodes.

Preparation of PES-LIG on a Porous Ultrafiltration or MicrofiltrationMembrane

LIG-PES membrane made from a commercial membrane (Nadir MP005, MicrodynNadir) with a VLS 3.50 (Universal Laser Systems) laser platform,equipped with a 10.6 Lm CO₂ pulse laser (50 W). The same image densityof 70 PPI (pulses per inch) and scan rate of 39% was used for all testswith 5% laser power. LIG-PES membrane was made in ambient environment inpresence of air, the general atmosphere within the laser platform wasstill air (1 atm).

A uniform black conductive LIG membrane coating was observed across theirradiated part of the membrane. The Raman characterization for theLIG-PES membranes showed similar 2D, G, and D peaks to the PES-LIG.

Fabrication of PSU, PES, and PPSU Laser-Induced Graphene (LIG) from PSU,PES, and PPSU Films

For thin films of PSU and PES, the polymer pellets (2.5 g) weredissolved in dichloromethane (20 mL) and the solution was poured into aglass Petri dish (inner diameter 11.5 cm). To slow the evaporation ofthe dichloromethane, an inverted funnel was placed on top of the petridish. For PPSU, the polymer pellets (2.5 g) were dissolved in DMF (20mL) and the solution was poured into the glass Petri dish (innerdiameter 11.5 cm). The solvent was evaporated under vacuum at 60° C.When the solvents were completely evaporated, the films were removed andmeasured to have an average thickness of 94.6±5.5 μm for PES, 102.5±4.2μm for PSU, and 106.6±7.4 μm for PPSU.

For the generation of LIG on the surfaces, a VLS 3.50 (Universal LaserSystems) laser platform, equipped with a 10.6 μm CO₂ pulse laser (50 W)was used. An image density of 70 PPI (pulses per inch) and a scan rateof 25% were used for all tests with variable laser duty cycle: ForPES-LIG and PPSU-LIG the Laser was focused (5% laser duty cycle), whilefor PSU-LIG, the laser was defocused by 0.4 cm with an 8% laser dutycycle, meaning that the PSU film was moved 0.4 cm closer to the cuttinglens from a focused position. PSU-LIG, PES-LIG and PPSU-LIG were made inambient conditions in the presence of air. The general atmosphere withinthe laser platform was still air (1 atm). A nozzle provided with theinstrument was used to blow air towards the laser spot.

The LIG on polysulfone (PSU), polyethersulfone (PES), andpolyphenylsulfone (PPSU) films were transparent and flexible. XRD andRaman spectroscopy indicated that the LIG was successfully made, and XPSindicated that the elemental composition of the LIG layer was carbon,oxygen and sulfur. Scanning electron microscopy showed the surfacestructure and compared the LIG made from PSU, PES, and PPSU, crosssections, and TEM. Morphological differences were observed: LIG madefrom PES and PPSU contained more long needle-like structures, while LIGmade from PSU had a more globular-like appearance. The XPS deconvolutionshows that new sulfur bond types were present in the LIG with new peaksat ˜164 eV compared to the substrate aromatic polysulfone material.

The hydrogen peroxide generation of these electrodes was tested asbefore. The hydrogen peroxide generation was more efficient than LIGelectrodes made from polyimide for example. PSU-LIG gave the highestamount of hydrogen peroxide of ˜2.6 mg/L after 3 hours of operation at2.0 V, using an aqueous NaCl (0.05 M) solution. Using an aqueoussolution of Na₂SO₄ (0.05 M), PPSU-LIG gave the most H₂O₂ production at˜1.8 mg/L after 3 hours.

The biofilm inhibition of the surfaces was tested as in the aboveexamples using P. aeruginosa, and similarly as above, all LIG surfacesshowed almost complete inhibition of biofilm growth.

The surfaces as electrodes were tested similarly to the examples abovefor the ability of the LIG electrode surfaces to eliminate bacterialviability in solutions using voltages of 1.5-2.5 V. In these cases, themost effective voltage used was 2.5 V, and the bacterial solutions wereeffectively decontaminated within 2-4 hours of operation. These surfaceswere more effective than that of the LIG made from polyimide in that itkilled the bacteria in a shorted time period.

Preparation of LIG on Porous Ultrafiltration or MicrofiltrationMembranes, and Performance Testing as a Filter and in a StackedFilter-Electrode Configuration

PES ultrafiltration (UF) membranes were made using common phaseinversion techniques as known in the art. Briefly, the membranes weremade by casting a 16% w/w PES solution in NMP on glass and named as PES1membrane or on a nonwoven polypropylene support named as PES2 membranewith the casting knife adjusted to a layer thickness of 150 μm, followedby immersion in a water coagulation bath (20° C.). Membranes were keptin DDW water for at least 24 h to complete the phase inversion process.The PES UF membranes were then air-dried and LIG was achieved on thesurface using the same laser (50 W) with settings 0.1% laser duty cycle(70 PPI image density and 25% scan rate).

Membranes and LIG-membranes were characterized by ATR-FTIR, SEM, andcontact angle before and after laser modification. Membranes were soakedin DDW water for at least 4 h and then used for different applications.Using the same settings, LIG was also made on commercial membranes fromMicrodyn-Nadir: UH050, UH004, MP005 and UP150 and these were also usedfor filtration as LIG-coated filters.

The LIG filters were tested for the ability to filter bacterialsolutions. A mixed culture of bacteria taken from the secondary treatedwastewater aeration pond near Sde Boker (Israel) and was grown in LB.The bacterial concentration was adjusted to 10⁶ CFU/mL and 10 mL wasvacuum filtered through the filter at 0.5 Bar. Bacteria quantificationwas performed with the plate count method for the feed solution and thepermeate. The bacterial removal was highest using LIG filter type PES1and PES2, which removed between 70-95% of the bacteria.

To demonstrate again the antibiofilm ability of the LIG as made on apolymer filter, the LIG coated UP150 filter was subjected to biofilmgrowth condition as reported above. The mixed bacterial culture wasused. The LIG-UP150 coated filter had almost no biofilm growth, comparedto thick growth on the uncoated UP150 membrane filter.

A graphite wire was attached to the LIG surface of the LIG coatedmembranes circular coupons (46 mm diameter) using a carbon-based glue.An epoxy glue was used to strengthen and protect the connection. Two ofthese membranes were stacked and assembled in a 500 mL vacuum filtrationapparatus, and connected to a direct current (DC) power source with thebottom membrane as cathode and the top as anode. Using a vacuum pump toregulate the flow, the mixed bacterial culture suspension (˜10⁶ CFU mL⁻¹in 0.9% NaCl solution) and were added and 15 mL of contaminated waterwas passed through the filtration unit at a rate of 1500 LMH. Theexperiments were done at room temperature at 2.5 V. Bacteria werequantified using the plate count method for the feed solution and thepermeate. In all cases a 6 log removal of bacteria was observed(complete decontamination). Using the UP150-LIG membrane stacked filtersat an ultra-high flow rate of 22000 LMH, ˜6 log removal was observed at20V.

Additional Usages

The PSU class polymers are the most highly used material in membranefabrication due to mechanical and compressive strength, thermalstability, and chemical inertness over the entire pH range enablingwidespread use in most separation applications. Moreover, these polymersare prevalent in many other aspects of society including microelectronicdevices, thin film technologies, fuel cells, and biomaterials. Themethods of the present invention directly generate conformalsulfur-doped LIG on this PSU-polymer class in a single step,fundamentally a solvent- and reagent-free technology. Biofouling ofsurfaces is especially challenging in membrane technology in which LIGcoatings could be game changing. The electrochemical and antifoulingproperties of the flexible sulfur-doped LIG might also be effectivelyused for in-situ decontamination and degradation of emerging pollutantsin water and wastewater, for fouling resistant cathodes in microbialfuel cells, or as porous flow-through electrodes for capacitivedeionization: broadly applicable in the energy, biomedical, andenvironmental fields.

PSU-LIG and PES-LIG and PPSU-LIG can be used to fabricate electrodes asboth cathode and anode.

The voltage applied across the electrodes for production of chemicalspecies may be in the range between 0.05V to 20V, preferably between 1.5V to 2.5 V, inclusive.

The amount of chemical species may be controlled by adjusting thevoltage or by alternatively turning on and off the voltage. The in-situgeneration of H₂O₂ and other bacterial toxic species and the ability tocontrol their amount provides precisely enough antimicrobial componentsto eliminate or minimize the formation of viable microorganisms,biofouling or biofilm growth. The ability to control the amount ofchemical species also limits degradation of possible nearby membrane orother materials. Adjusting the voltage on these surfaces while inaqueous solutions that contain microorganisms in effectively kills theorganisms and can be considered an “active” form or antimicrobialaction. For example, electrodes consisting of PSU-LIG or PES-LIG orPPSU-LIG at voltages between 1-5 V, preferably between 1.5-2.5 V placedin solution containing bacteria, for example 10⁶-10⁷ CFU, reducebacteria population between 2-7 log reduction.

The PSU-LIG and PES-LIG and PPSU-LIG exhibits antibiofilm properties.This prevents fouling of surfaces, biofilm growth and bacterialattachment on the surfaces. Bacterial survival after contacting the LIGcomponent is generally below 85%, and preferably is below 0.1%.Therefore, in another aspect the present invention is directed tomethods of preventing or reducing or minimizing fouling, biofilm growthand/or bacterial attachment on elements of water treatment systems.

Direct 3D Printing of Graphene Materials from Carbon Precursors

In further embodiments, the present invention relates to direct 3Dprinting of graphene materials from carbon precursors. The presentinvention includes a metal-free method by which a 3D graphene object canbe printed via the exposure of one or more carbon precursors to laserirradiation. Single exposures of a laser can be employed, but,preferably, multiple exposures can be used.

Method of the present invention include lasing a mixture (preferrablypowdered) of the following:

-   -   A. One or more graphitizable thermoplastic polymer (PPS, PEI,        PEEK, PES, PPO, or similar);    -   B. Optionally, An additional non-thermoplastic carbon precursor        for laser-induced graphene (activated carbon, themoset polymer,        or other source of carbon);    -   C. Optionally, additives to modify the properties of the 3D        graphene (can be powder or liquid.

The use of an appropriate thermoplastic polymer is sufficient to obtaina 3D graphene structure. For example, polyphenylene sulfide (PPS),polyetherimide (PEI), polyethersuflone (PES) or polyether ether-ketone(PEEK) powder can be used. The thermoplastic polymer powder is exposedto laser irradiation and the particles of the polymer are fused. Forinstance, this can be performed in two ways. First, the polymer powdersmay be fused by selective laser sintering at lower laser powers to firstmelt the polymer powders into a solid structure without converting tographene. Following this step, additional exposure(s) to the laser athigher power would then convert the structure into graphene.Alternatively, a higher powered laser exposure can be applied to fuseand convert the polymer into graphene in one step. A scheme of thisfabrication process is shown in FIG. 41 (which is an embodiment of asimple implementation of 3D printing of graphene using a thermoplasticpolymer powder (polyphenylene sulfide)).

In the implementation shown in FIG. 41, an initial layer ofthermoplastic polymer powder is added onto a surface. Acomputer-controlled laser beam is then scanned across the powder withthe laser beam turned on only within boundaries of pattern. The patternincludes a cross-section of the larger 3D structure that is to beprinted. Additional powder can then be applied by sprinkling, smearing,or shaking either manually or by using an automated powder dispensingmechanism. After application of the new layer of powder, the laser isthen scanned within the boundaries of the next cross section of thelarger 3D object to be printed. Repeating this process for subsequentlayers results in a 3D structure consisting of laser-induced graphenematerials.

The choice of the mechanism for dispensing and dispersing the powder ofthe surface of the working area for the laser exposure may varydepending on the mechanical properties of the powder mixture. Namely, ifthe mixture is free-flowing and suitable for 3D printing, all standardmethods for dispensing powders will be viable whereas if the materialclumps together a mechanism for sprinkling the powder will be required.

Raman characterization of the obtained 3D structure confirms that thematerial has been converted into LIG. As previously discussed, thenumber of exposures to laser irradiation does impact the quality of thematerial obtained with an optimal number of laser exposures that mayvary depending on the precursor material. See FIG. 33 (which shows thatrepeated lasing of the polyetherimide carbon precursor results in higherquality graphene as evidenced by the increase of the 2D peak with thenumber of lases as well as a better D to G peak ratio).

While the use of a thermoplastic polymer alone is sufficient to obtain a3D graphene structure, a preferred embodiment includes the use of amixture of a thermoplastic polymer material with a non-polymeric carbonsource such as activated carbon, activated charcoal, biochar or similarmaterials. Non-thermoplastic polymer materials such as polyimide,polybenzimidazole, phenolic resins, lignin, or similar materials canalso be used. Using such a mixture, a material with higher conductivity,specific surface area, robustness, and other beneficial properties canbe obtained as compared with the use of a single polymer precursor.Activated carbon readily forms 3D graphene as shown in the TEM imagesbelow (FIGS. 42A-42B) and has a high surface area. However, activatedcarbon does not adhere together well during 3D printing precluding itsuse as a singular material in 3D printing.

A specific example of this implementation of the 3D printing of LIG isas follows. 5 grams of polyphenylene sulfide powder with averagemolecular weight ˜10,000 (PPS) was mechanically mixed together with anequal amount 100-mesh Darco activated carbon (AC). A 3D structure wasthen obtained using the method described in FIG. 41 using a UniversalLaser Systems laser cutter (Model XLS10MWH). The CO₂ laser (10.6micrometer wavelength) was used in the raster mode with a 1000 DPI pulsedensity. The power used was 5% power (˜3.7 W) and the speed was 5% ofthe maximum speed of the XLS10MWH laser cutter system.

The sheet resistance measurement of a few layers of the printed materialwas measured using a 4-point probe. The measurements showed that thematerial was extremely conductive with a sheet resistance of <5Ohms/square. Raman spectra of FIG. 43 shows that the material isconverted to laser-induced graphene which is consistent with the highconductivity of the 3D printed material.

This method of forming laser-induced graphene could be performed inambient atmosphere, which was unlike many previous methods that requirea controlled atmosphere.

This mixture allows for a one-step process for obtaining 3D graphenestructures without requiring time-consuming thermal treatment in a CVDfurnace or an acid etch to remove metal catalysts.

FIG. 44A is a photograph of a 5 mm³ 3D graphene monolith printed fromPPS-AC using a powder bed printing method. The bulk conductivity was 20S/m. FIG. 44B is an SEM image of a corner of the cube shown in FIG. 44Aat 50× magnification (scale bar is 1 mm). FIG. 44C is an SEM image ofthe surface of the cube shown in FIG. 44A (scale bar is 50 μ.m).

FIGS. 45A-45C are photographs of freestanding graphene objects printedusing a 50/50 mixture of polyphenylene sulfide and activated carbon withfeatures less than 1 mm in width (scale bar is 1 cm). FIG. 45D is aRaman spectra of a PPS-AC graphene object.

FIG. 46A is a schematic of 3D printing box 4600. The printing box 4600includes a laser 4601 that can move in the x and y direction. Buildingin the z direction is performed by adjusting the build volume (or buildarea) 4604. Printing box 4600 further includes a powder reservoir 4603containing powder that is distributed by powder distributor 4602. As thebuild volume 4604 is adjusted, the powder is distributed by the powderdistributor on top of the previously lasered powdered (for furtherutilization of the laser 4601). FIG. 46B is a photograph of a powder bedbox 4605, which shows the build area 4606, the powder reservoir 4607,and the powder distributor 4608.

FIG. 47A is a schematic of a 3D printing box 4700. FIG. 47B is aschematic of 3D printing box 4700 in a controlled atmosphere chamber4701. FIG. 47C is a photograph of a 3D printing box 4702. FIG. 47D is aphotograph of 3D printing box 4702 in a controlled atmosphere chamber4703. FIG. 47E is a photograph of 3D printing box 4702 in controlledatmosphere chamber 4703 with a ZnSe window 4704.

Utility and Variations

Graphene, a 2D single-layer of carbon, has attracted intense interestdue to its large specific surface area, high electrical and thermalconductivities and superior mechanical strength. It has been used invarious applications, such as in electrodes for supercapacitors andlithium ion batteries, transparent conducting films, and photocatalysis.However, in energy storage device and mechanical related applications,individual 2D graphene nanosheets need to be integrated into 3Dmacroscopic structure, as 2D graphene often does not meet the mass andvolume requirements.

Free-standing 3D printed frameworks containing laser-induced graphenewould have applications in supercapacitors, lithium ion batteries,lithium ion capacitors, catalysts for water splitting into H₂ and O₂,water-oil separation, water/gas purification, sensors and mechanicaldampeners. The 3D printing method using a mixture of carbon precursorswould allow a structure with high specific surface area, goodcrystallization, a mechanically robust structure, and good electricalconductivity to be obtained.

The method of the present invention is unique in that the processinvolves the direct conversion of carbon precursors into laser-inducedgraphene by multiple exposure to laser irradiation. This removes thenecessity of a prolonged etching period (multiple days) that previousmethods using metal catalysts required. No additional thermal treatmentsor drying steps are required since this procedure is a one-step processfor obtaining a 3D-graphene structure. The material will also be free ofany metal contamination. Results also show that this method yields anobject that is more robust mechanically than the previous methods.

Moreover, there are significant advantages for use of a mixture ofthermoplastic and non-thermoplastic carbon precursors in the methods ofthe present invention. Exclusive use of thermoplastic polymers, such aspolyphenylene sulfide (PPS), polyetherimide (PEI), or similarthermoplastic polymers, can successfully result in the formation of alaser-induced graphene containing 3D structure. However, there aredrawbacks to this approach, including the fact that such a mixture tendsto deform when exposed to the laser. This can cause a large reduction inprint accuracy and resolution. Potential reasons for these issues arethe volume change of the polymer as it is being converted into graphene(some material is ablated) as well flowing of the material as it melts.One can program this into the laser movement so that a final structureto the desired size could be made.

Non-thermoplastic carbon precursors, such as activated carbon, haveminimal volume and shape change compared with the thermoplastic polymersbut do not sinter together. This means that a 3D-printed objectincluding solely these types of materials tend to have very poormechanical robustness often falling apart spontaneously.

By mixing the two materials, it is possible to achieve the advantages ofboth. In this case, the thermoplastic polymer serves as a binder thatwill melt during the laser sintering process. Additional lases asdescribed in the multiple lase method then convert both thethermoplastic material and the non-thermoplastic material intolaser-induced graphene.

Potential advantages also include:

-   -   A. Increased surface area from activated carbon or other        non-thermoplastic precursor.    -   B. Reduced volume change during lasing (less deformation of        printed object).    -   C. Mixture is more free flowing (more suitable for 3D powder        printing).    -   D. Enhanced conductivity of the resulting structure (from        activated carbon).    -   E. Higher resolution and print accuracy.

Further variations also include:

Controlled Atmosphere—

From a scalability standpoint, operation in ambient atmosphere would bethe most advantageous. Preparation of material in a controlledatmosphere, such as an inert or reactive atmosphere, may be utilized toalter the functionalization of the graphene materials. For example,preparation in a reducing atmosphere such as H₂ would lower the amountof oxygen containing functional groups and potentially make the surfaceof the material more hydrophobic. Controlled atmospheres may be used totune the hydrophilicity of the surface. Oxygen, SF₆, nitrogen, argon,and other gasses may be employed instead of ambient atmosphere.

Additives—

Various metal additives such as Ni, Cu, Ni—Cu alloys, Ru, Ag, Fe, or Co,for example, could be added to give the 3D printed structure newproperties such as catalytic activity for various reactions. These couldbe added as salts prior to lasing, or electrochemically adsorbed afterlasing. Other additives such as melamine, ammonia, boranes, phosphenes,and phosphides (alone or in combination) could be added to obtain doped3D graphene structures.

Liquid Precursor Materials—

While using a powdered system, laser sintering appears to be the mostfacile method of obtaining a 3D graphene structure. Conversely, onecould use other 3D printing methods in conjunction with multiple lasingsto obtain similar results. For example, a slurry containing athermoplastic polymer, a solvent, and optionally the non-thermoplasticpolymer could be printed using a slurry method of 3D printing followedby exposure to a laser. Alternatively, an extrusion method could beemployed wherein a filament of the thermoplastic material containing theoptional non-thermoplastic precursor is melted and extruded. Thematerial extruded could then be lased. If the thermoplastic material issoluble in solvents, a solution of the thermoplastic material could besprayed over particles of the non-thermoplastic material. Certainpolyimides especially fluorinated polyimides would be suitable for suchan application.

REFERENCES

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While embodiments of the invention have been shown and described,modifications thereof can be made by one skilled in the art withoutdeparting from the spirit and teachings of the invention. Theembodiments described and the examples provided herein are exemplaryonly, and are not intended to be limiting. Many variations andmodifications of the invention disclosed herein are possible and arewithin the scope of the invention. Accordingly, other embodiments arewithin the scope of the following claims. The scope of protection is notlimited by the description set out above.

The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated herein by reference in theirentirety, to the extent that they provide exemplary, procedural, orother details supplementary to those set forth herein.

1. A method of producing a graphene material, wherein the methodcomprises: (a) selecting a material comprising a carbon precursor; (b)converting the carbon precursor into laser-induced graphene by utilizinga laser having a focal plane to subject the carbon precursor to morethan one exposure of laser irradiation and wherein the step of utilizingthe laser is selected from the group consisting of (i) utilizing thelaser to perform multiple lase passes over a same area of the material,(ii) utilizing the laser upon overlapping regions of lased areas of thematerial, and (iii) combinations thereof.
 2. The method of claim 1,wherein the step of converting the carbon precursor into laser-inducedgraphene is performed at ambient conditions.
 3. The method of claim 1further comprising applying a heat source to the material to char thecarbon precursor before the step of converting carbon precursor intolaser-induced graphene.
 4. The method of claim 3, wherein the heatsource is a flame.
 5. The method of claim 1, wherein the materialcomprising the carbon precursor is selected from a group consisting ofpolymers, lignin-containing materials, cellulose-based materials, andnon-polymeric sources of carbon.
 6. The method of claim 1, wherein thematerial comprising the carbon precursor is an polymer selected from agroup consisting of polyphenylene sulfide, polyamide-imide,polybenzimidazole, phenol-formaldehyde resin, poly(ether ether ketone)(PEEK), poly(m-pheylenediamine) isopthalamide, crosslinked polystyrene,epoxy, and poly(ether-imide).
 7. The method of claim 1, wherein thematerial comprising the carbon precursor is a lignin-containing materialselected from a group consisting of wood, coconut shells, potato skins,and burlap.
 8. The method of claim 1, wherein the material comprisingthe carbon precursor is a cellulose-based material selected from a groupconsisting of cotton cloth, paper, cotton paper, and cardboard.
 9. Themethod of claim 1, wherein the material comprising the carbon precursoris a non-polymeric source of carbon selected from a group consisting ofamorphous carbon, charcoal, biochar, activated carbon coal, asphalt,coke, and Gilsonite.
 10. The method of claim 1, wherein the step ofconverting the carbon precursor into laser-induced graphene comprisesutilizing the laser to perform multiple lase passes over the same areaof the material, wherein the material is positioned in the focal planeof the laser.
 11. The method of claim 1, wherein the step of convertingthe carbon precursor into laser induced-graphene comprises utilizing thelaser upon the overlapping regions of lased areas of the material,wherein the material is positioned offset the focal plane of the laser.12. The method of claim 11, the laser is utilized at ambient conditions.13. The method of claim 11, wherein the utilization of the lasercomprises exposing the material to multiple lases in a single pass ofthe laser while the material is positioned offset the focal plane of thelaser.
 14. The method of claim 11, wherein the material is positionedoffset of the focal plane of the laser in an amount that is at least 1%of the laser focal length.
 15. The method of claim 11, wherein thematerial is positioned offset of the focal plane of the laser in anamount that is at least 2% of the laser focal length.
 16. A method ofproducing a graphene material, wherein the method comprises: (a)controlling a gas atmosphere; and (b) fabricating laser-induced grapheneby exposing one or more carbon precursors to a laser source in thecontrolled atmosphere, wherein the exposing results in formation oflaser-induced graphene derived from the one or more carbon precursors.17. The method of claim 16, wherein the step of controlling the gasatmosphere obtains a superhydrophilic laser-induced graphene or a highlyhydrophilic laser-induced graphene.
 18. The method of claim 16, whereinthe step of controlling the gas atmosphere obtains a superhydrophobiclaser-induced graphene or a highly hydrophobic laser-induced graphene.19-99. (canceled)
 100. A method comprising: (a) selecting one or morecarbon precursors; and (b) direct 3D printing of graphene materials fromthe one or more carbon precursors via the exposure of the one or morecarbon precursors to laser irradiation, wherein the laser irradiation isperformed utilizing a laser having a focal plane and wherein the step ofutilizing the laser is selected from the group consisting of (i)utilizing the laser to perform multiple lase passes over a same area ofthe material, (ii) utilizing the laser upon overlapping regions of lasedareas of the material, and (iii) combinations thereof.
 101. The methodof claim 100, wherein a metal catalyst is not required to produce thegraphene materials from the one or more carbon precursors. 102-119.(canceled)